I've noticed that the price of a used 50D has fallen to around $800, but the older used 40D seems to be be sticking around $700. Is the 50D that disappointing? I know that DPreview found that high ISO shots with the 50D were noisier. Is that the crucial factor? Or do people just want to pass right over the 50D for the 7D?
Canon EOS 50D Digital SLR Camera Review
I have never liked DPReview, reading their reviews is like trying to watch Fox News. There may be some good info in there sometimes, but you really have to wade around the crap and biases to actually find it.
Anyway, that link has an ISO comparisson test for the 50D and compares it against 40D and XSi. I've always found the-digital-picture as a great source for reviews on Canon products.
I've had a 50D since about June of this year and have been nothing but pleased with it. I'm not really motivated to get a 7D, but maybe I would be if I had a like a 20D or 30D.