eos 20D vs eos 400D

I see no reason to swap a 20D for a 400D. A 400D would make a decent backup for the 20D of course, as would the 350D.

I have a 20D that I'm very happy with. I haven't moved to a 30D, not because the 30D isn't better, but because it's not sufficiently different to make it worth the $500 or so I'd have to spend to to do the trade.

The 20D is better built, has 5fps, a larger viewfinder, a rear control dial, ISO 3200, a seperate top deck LCD and a few other features that the 400D doesn't. On the other hand the 400D has a larger LCD, an extra 1.9MP, picture styles and a dust removal system. On balance I'd take the 20D.