Over the past couple of years, the 20D started to feel more and more out of date. However, I never really saw a new camera hit the market that didn't feel like I was making a compromise.
The Nikon D800 hit the market in recent days. It has a gaudy 36.3 megapixels!! Wow! The amount of detail you can get with that kind of sensor would be amazing.
At the same time Canon came out with the Canon 5D Mark III which is a more expensive 22.3 megapixel camera. At first blush, it sounds a bit ridiculous to charge more for a camera with 14 fewer megapixels. However, as with all things, purpose sometimes outweighs everything. For example, if you need to haul lumber, you might go with a pickup truck over a Toyota Prius even if the Prius gets much better gas milage.
Since I am a one camera kind of guy, I needed a camera that could do everything I needed without a lot of fuss. The main thing that has been holding me back is the fact that full frame cameras have had slow shutter speeds in the consumer market. I wanted something to shoot fast moving pups, bees, birds, horses, etc.
The 6 frames per second speed of the Mark III was a meaningful step forward. The D800 can also produce 6 frames per second if you use the $415 (Amazon's price today) Nikon Grip (which brings the price closer to the Mark III). Also, even with the grip you would need to have a lot of battery power left to get 6 frames per second. However, you can't produce full RAW photos. From what I understand, you have to use DX mode which is equivalent to 15.3 MP. Also, the buffer is said to be slower, which would slow you down after you took your initial shots. Personally, I don't want the extra weight of the grip all the time and the DX factor would kill the one main stat that makes the D800 so special.
That being said, if I had Nikon lenses, I would have gone that route. The fact that I have Canon lenses and did not want to sell everything was a major decision in my choice, as well. Also, my dad shoots Canon, so losing access to his lenses also made the choice easier.
As you can tell, I ended up buying the 5D Mark III. Since I only buy a new camera once every 8 years or so, I felt it was worth the money, even if I think it is a bit overpriced compared to the Nikon D800. Also, I can sell some of my APS-C (only work on smaller sensors) lenses to help pay for it. Personally, I think it is a better "all around" camera than the Nikon and that was my main consideration. However, if I was mainly shooting landscapes, I would have had a harder choice to make.