Bobby,
Thanks for the link. My biggest problem with my 20D is the back focusing. For fish pics at aperatures from 11 - 22 it's not an issue. When trying to shoot deer in low light situations with an aperature of 2.8, it becomes a huge deal. The biggest problem is, since I don't own a 400mm 2.8 and can't justify spending the money, you can't see the slightly out of focus problems until the pictures are on the computer.
Wildlife and portrait shooting would be the big reasons for the upgrade for me. Plus, the ISO listed in the viewfinder. In the 20D, the ISO isn't shown in the viewfinder. I don't know how many times I've taken shots at 800 ISO then forgot to change back afterwards.
I don't have all the glass I need, but I intend to purchase new glass as well. Right now I'm trying to decide on 40D or 5D. 5D is full frame but costs a lot more, and I don't do a lot of landscape photopgraphy, more telephoto. So at this point the 40D sounds like the best choice. I'm just waiting unil more people are using it to hear more reviews than just those Canon geeks who love everything Canon does.
Tim