I have the 350d ( xti I thinks its also called ) and 40d. The image quality is identical in my opinion.

The feel is totally different though. I like the grip on 40d a lot. I first bought the 450d but it had backfocus issues and decided for a real upgrade, as my old 350d had 80 000 exposures or so.

Heres my lates onlocation shot of the band BluesUp at the local jazzclub, with a Vivitar285hv and the Sigma 10-20.