Just picked up a used 20D on Friday to substitute my XTi for many reasons.
Got familiar with it's different settings and how and where to set everything. Body is slightly larger and heavier and of course the non-plastic construction. I do have to say I am very inpressed with this next level body and it's performance and IQ.
I used it Saturday morning at my MMA class for belt testing and my 70-200 f/4 shot wide open, with action and some static moments and the images came out much better and had more keepers than with my XTi...and most importantly no blurry images!!! The 20D seems to perform better with action shots than the XTi does and with better IQ IMO.
The shutter is most different than the XTi...not sure if it's louder or not as it just has a more mechanical, profound...clack. I like it though.
Overall, I am most pleased with my decision to buy this several year old great performer 20D!
Time to sell the XTi...buh-bye!