Pros: super fast routing, very bright display, preloaded US detailed maps.
Cons: There really aren't any worth mentioning.
I bought the 550 to replace my trusty Garmin GPS V that I've been using for about 3 years now. I bought the V so I wouldn't have to worry about getting lost on the motorcycle in the North Georgia mountains. Compared to the V, the 550 is nothing short of magical. I have been using it now for about 3 weeks so I'm still in the 'honeymoon' stage but I really love this GPS. Two of the best things are its blazing calculation speed and having the entire US detailed maps already loaded on board. Spending 40 minutes or more to download a few detailed maps to the V before going on a trip was something that I just did as part of a pre-trip preparation. Now, I don't have to worry about that. Additionally, I now have details over the entire route instead of only in the parts that I chose to download. I do quite a bit of long distance riding so that is a wonderful plus to me.
Right out of the box, which includes an amazing amount of stuff to get the unit mounted in both auto and cycle, the unit fired right up. It asked me a couple of questions about language preference and time zones then went to work. I bought a 2 GB SD card for it and it works great.
The car mount works very well also. I have a bluetooth capable cell phone and the car mount acts like a speakerphone. If you have a bluetooth headset, the 550 will use it to notify you of your next turn while following a route. If you don't, or it is off, the 550 will say the turns using the speaker in the auto mount. I was a little suspect about how strongly the auto mount's suction cup would adhere to the glass. After struggling a little the first time I took it off to move it into another car, I quite worrying.
The motorcycle mount is very good also. I guess my only complaint would be that the 550 is so large it is hard for me to find the perfect spot to mount it so that I can still see all of my gauges and lights.
The display is very bright and easy to read even with sunglasses on. The large buttons on the touch screen make it very easy to find what you are looking for. The 550 also makes finding things easier by guessing what you are looking for as you type. For example, tell it you are looking for a city and then start typing the name. If there are only a few cities with that name, it will pull them up as soon as it realizes that fact. It even will do partial matching after you hit the enter button.
I would recommend this unit to anyone who does a lot of traveling on a bike.