When we brought the Treo 600 into our office a little over a year ago, I wrote a review here on Epinions of the device from the perspective of a sys admin (http://www.epinions.com/content_129584238212). The 650s are out this year and we have three new devices in the office now - one of them exclusively just for me (partly just so that I can learn it better to help the others in the office that have them).

So now I will go through the same things I did before, but on the new one.

The Good
1) Looks. This thing looks fantastic. I liked the way the 600 looked, but this one is even nicer in my opinion. There is more chrome and it is slightly curvier. The size and weight of it is close enough to the 600 that it isn't drastically different, but you can definitely notice a change. A change for the better if you ask me. After discussing it with the other users here, they feel that it is smaller and lighter than the 600 - the antenna on it is definitely smaller (although still sticks out).
2) The power cord. The wall wart side of the power cord is designed so that it can be put at the end of a power strip and not block other outlets, or it could be put into the wall and not blow others. It is still slightly cumbersome because it causes the bulk of the wall wart to push off to the side, but it works well at my desk and I appreciate that. It connects well to the Treo as well - it reminds me of a better engineered version of the Sony/Ericsson T616's power cable (that is the phone I had prior to this Treo 650).
3) Networking galore. There are what appear to be about 15 ways of networking this device and I am only interested in a few of them. Note that if you want to be able to use Bluetooth to connect your computer (usually a laptop really) to the Treo and then on to your data network - as of this writing, it is only available in the unlocked version of the phone. The carrier branded versions (at least the US ones) have all turned that off which has caused a lot of anger out there in the phone nerd world. I have data access with my phone service, so I turned that on. I went into networking and set the APN to "proxy" (that is for ATT Wireless). I then fired up the web browser and hit Slashdot as a test - sure enough it worked straight away. Very nice.
4) Email. Part of my dislikes for the Treo 600 was that it wouldn't esily integrate with MS Exchange. Well, PalmOne did something nice and made an agreement with Microsoft so that it can use the ActiveSync with Exchange 2003... nice! After setting up Exchange 2003 to do mobile access and setting up users to be able to check/send via it, I can now check and send mail through our Exchange server via a secure connection. It of course will also connect to regular POP3 like the Treo 600 did, and you can have multiple accounts, each checking at different intervals and each in separate Inboxes. In the past, checking email over POP3 was okay, but getting it to send through our firewall caused issues. This is so much nicer/easier.
5) Removable battery. The 600 had it built in - the Treo 650 allows you to remove it which is nice for a variety of reasons. You can carry spares on long trips away from power sources, and if it dies on you (batteries have fixed lifespans) you can replace it. Do note that it is a bit annoying when you go to register and you have to take the battery out of the phone in order to get to the serial number.
6) The screen resolution is FANTASTIC - so very much better than the 600. The camera hasn't been improved at all, but the pictures look so much better due to the screen that you view it on having a better resolution. Many users of the device don't understand resolution at all - so this is essentially just magic. Fine by me - it looks terrific.

The Bad
1) I noted that the new power supply (charging unit) under part of the "Good". It is also part of the bad unfortunately. The old Treo/Palm devices had the power plug into the wall, and then into the sync cable on the USB side. That means that it would add some bulk down where it connected to the computer. But at that point the connection is solid and stable, so it is not a big deal. But the new setup, if you want the sync cable in there and the power too, then you have to put the power cable into the sync cable right at the base of the Treo. This adds bulk and weight which makes it easy for the Treo to get knocked off of tables where you have it resting while it charges. I have already done it a few times and it is annoying to see a $700 phone get dropped, purely due to a poor design choice. There is likely a cradle option available, but it doesn't come with the phone, and I don't have one, so I can't speak to how well that works or not.
2) The install software (in order to be able to sync with your machine) requires the machine to be restarted. This might not be a big deal for some people - but as a sys admin it bugs me to a huge degree. I hate having to restart a machine and I like to get a lot done at the same time - restarting because I installed this program means that I have to do one thing at a time and close the rest out. That is just stupid. Even on my Mac it requires a restart.
3) The ringtone volume is actually too loud for me. You can adjust it, but even at the lowest possible setting, it is still too loud. Because of that, I will probably leave the device in silent mode most all of the time and rely on the vibration feature of the phone (which is nice, but most all phones these days have vibrate).
4) No mp3 ringtones built in. There are two arguments against this being bad - 1) "who cares", which is valid, but I still want mp3 ringtones, and 2) there is software out there which you can buy and add on which allows you to have mp3 ringtones - were PalmOne to put that in as a feature, then the people that wrote the helper program would be out money... whatever, I want mp3 ringtones built in. Certainly not a dealbreaker, more of a nitpicky issue.
5) Apparently a lot of people are finding that the software which they used on their Treo 600 doesn't work on the Treo 650 and causes crashes/freezes and complain about the stability. I don't tend to install much on the devices I have, so this isn't a big deal to me - but I know that it is going go cause me headaches soon with the other users in the office who insist on installing all kinds of junk and then they will complain to me when it crashes, as if it is my fault. I am hopeful that this will all be resolved once the 650 has been out longer.
6) No WiFi. I personally don't really care if the thing has WiFi in it or not, but one of the users here is already complaining about it and he doesn't even have his phone yet. Because of that, I have to deal with this guy complaining, therefore the Treo not having it makes my job that much more annoying. Perhaps this point is less on the bad side of the Treo and more on the side of my job.
7) Branding and locking. As of this writing, there are Cingular and Sprint branded versions of this phone. They are locked so that if you have one, you can only use it on their network. So say you work in NYC and have a Cingular/ATT branded phone and you frequently travel to the UK, you can't then get a cheaper Orange service and swap out SIM cards when you are there. You have to rely on roaming and higher rates. Which is good for the carrier, and bad for you. You can buy the unlocked phone like what I got (and what I recommend), but it costs more. Also, only the unlocked phone can do the dial-up networking over Bluetooth.

Other things to note
Here are some things that are neither good or bad, but just ... well, they just are things I have made note of but don't realy have an opinion - but would want to know prior to buying the device.
This is an unlocked model (purchased that way). There are rumors going around that there is a keyboard method to unlock the branded versions, and when you use that it does say on the screen that it is unlocked, but then the "unlocked" functionality is not there. It is highly unlikely that there is just a keyboard event which will unlock it - if and when that ability is exposed, it will be via a software/firmware update. As it stands now, I am not aware of one - and for the ovbvious reason that I have an unlocked one now.
It comes with a USB sync cable, a power cable, a single ear headphone device (wired), a sheet of screen protecting plastic (which I am opting not to use since you have to cut it by hand, following one of the patterns on the back, and I am far too lazy for that), a massive user manual, a small flier about accessories which you can buy for your new device, and CDs for the HotSync software for Mac and Windows (a separate one for each).
The stylus on this version is different than the Treo 600 - there are no moving/removable parts on this one - it is just a single shaft with a plastic bit at the end. Part of this is because you no longer need to disassemble the stylus in order to reset the device, it is more easily hit now (for good and bad I guess). But it also means that if the plastic bit at the end breaks or wears down to be unusable, it appears you need to replace the entire stylus whicih feels nice enough in the hand that I am guessing it is awy more expensive a replacement than just the plastic tip.
When I took my SIM card out of the T616 and put it in the nice little sliding tray on the Treo 650, I pushed it into the device and it then went and found my service and played the ascending notes of "your phone is on" notification. When I yanked the SIM card slot out right after that, it then played the descending notes of "your phone is off" notification. When the SIM card is in and I looked at the info screen for the phone, it told me "number not on SIM" - meaning it doesn't have my number. Yet the phone works. Not sure what that is about.
Syncing via the cable with an XP system seems even faster than with the Treo 600 - or perhaps I am just hopeful. I have yet to sync over Bluetooth. I tried setting it up on my Powerbook and with both of the devices in autodiscover mode, I set them up so that they are aware of each other, but the Powerbook didn't know what to do with the phone other than identify it. So that means I need to install the software from the CD first, which then requires a reboot - and I hate rebooting.
Battery life appears to be great, and it looks to charge in less than 4 hours (although the manual says it takes 4).
The device causes pocket sag. It is still of the size/weight that having it in a shirt pocket or pants pocket causes a tug there. This is less of an issue in the winter when I always have slacks on, usually a shirt with a pocket, and a jacket. But in the summer when shorts come out and shirts without pockets, it makes it harder to carry around. This is more of an issue in a casual atmosphere, which we have here in Bermuda.
The keyboard is much easier to use than the Treo 600, as my users tell me, but as a new user myself it is still taking a bit to get used to. I know that some grow out their thumbnails a bit in order to use those.

Two things that I have yet to see enough of and therefore am unsure if they are a worry or not:
When you connect to mail, the network shows as active. Then when you are done with the network (same goes for the web) it still shows active (green arrows by the signal strength meter). It isn't clear to me if that is actually sending/getting anything, which would cost me money, or if it is just letting me know there is a network there if I need it.
The other thing that I am not sure about is with the ActiveSync with Exchange 2003 - it warns you that it will assume that the server is right and therefore whatever the server has will win out when it updates calendar info. My users, when I explained this to them, did not get what that means. I think I can see this resulting in headaches down the road - but here's to hoping that I am wrong.

Overall, I didn't think the Treo 600 was worth it and didn't want one.
But the Treo 650 is fantastic and other than its size/weight making it less than ideal for carrying around, it is quite nice.
I definitely recommend this unit to anyone that wants to have a networked phone with a full keyboard.

Recommended: Yes

Amount Paid (US$): 700