Pros: Dedicated ISO/WB buttons, better diopter
Cons: Same metering issues as D40
I've been using the D40 for about a year and a half now, and have been getting some great images with the 18-200mm VR lens. Six megapixels are plenty for the size of prints I make, but I wanted a bit more cropping flexibility and still retain a near-300 dpi print res (or greater) at 8.5" x 11". Since the D200 was nearly impossible to find in stores, I opted for the D80 and 18-135mm kit lens. And, impatient fool that I am, didn't want to wait for an online shipment (that would have saved me a considerable amount), I paid a visit to Best Buy and got the last one in stock.
First thing that struck me was the difference in size and weight compared to the D40. Which, in my opinion, is NOT a bad thing. I'm old school; full-sized metal-bodied 35mm SLRs such as the older Praktica and Pentax models are still my favorites. I like big and heavy. The second thing I noticed was the plastic mount on the lens (same as with the 18-55mm lens that comes with the D40). I DON'T like plastic. So, the 18-200mm VR went straight to the D80 (and effectively doubled its weight, it seemed). My D40 now sports the lighter 18-135mm, and talk about a light, sweet setup! I'll hang onto it for fun. Third, I noticed the diopter adjusted a little better than the D40, so images appeared sharper when shooting without glasses.
I've set the D80 pretty close to how my D40 is set up, and a big plus is having ISO and white balance adjustment buttons (adjustable by using the rear jog wheel), instead of having to go through the menus. I like the LCD screen on top, too...battery life is extended somewhat, since that nice, big rear LCD is used for reviewing your shots (and occasionally making menu adjustments), and stays off most of the time. The included screen protector is a nice touch. Shooting adjustments (aperture, ISO, WB and such) are read off the top LCD, which can be back-lit using the power switch, another nice touch. Yet another added plus is the depth of field preview, but I find it a bit awkward to use...I either have to switch my grip from the focus or zoom ring, or stretch the ring finger of my right hand, to reach it with my stubby little fingers. A very minor issue is the D80's "OK" button being located where the "Delete" button is on the D40. That took a bit of getting used to.
I've read complaints regarding Nikon charging extra for their raw processing software (it comes with a trial version), but this isn't an issue with me since I don't waste my time shooting raw. The D80 also shares the D40's propensity to shoot a little over exposed in some cases. But, after a year and a half with the D40, I've learned to work around that. Hey, that's why there's exposure compensation. It also uses SD cards, same as the D40. Lastly, the D80 gives the same great image quality as the D40, and has the added advantage over it by having the AF motor in the body instead of the lens, making it more compatible with the older Nikon AF lenses.
The D40 is a great little camera; if you really need the extra resolution, the D80 is a logical choice if the larger size and greater weight don't bother you.
Update, 11/20: On 11/14, I had been doing a bit of shooting around the house, and found a hot pixel as I was editing. I went back to the retailer, and made an exchange with no hassle whatsoever. Kudos to Best Buy!