This kind of topic has been beaten to death so many times! Either way, it has always come down to what features you need, as in what your print sizes generally are and customer base along with a person's style of shooting and general interests in photography. Sure, most people would love to have a large FF sensor, but there are others who enjoy the 1.6 crop to get that extra free reach. (ie: birding, field sports, etc)
JulesMaximus, I'm with you when you say you'd never buy an EF-S lens!
I have a 300D right now, but am moving to a 1D series next year. (anticipating a 1D-MK2N successor) I shoot a wide variety of shots from sports to portraits and am also delving into weddings before this year's end.
Anyways, a 20D is no slouch, no matter how you slice it and dice it. The photographer always has and always will be the deciding factor on the quality of the image; not the camera body.