Hi,
I have been using the 450d for about a year now and have been quite impressed with the camera in general. Image quality, I think, is good enough. Compared to my first digital, a 20d the resolution was 'just right' for me. But I do notice more noise even at low iso's. Have been using it a lot lately doing literally hundreds of packshots for a website. Using live view and man focus. Worked great. Got a 5d2 two weeks ago with the 24-105 zoom. Fantastic feel and build quality. But very heavy and bulky.
The 450 with a 35mm f2 is very light and small, like a poor mans leica... The 50d is more like the 5d2. also I have this 'feeling' that 12mp is the optimum for 1.6 crop camera, as is about22mp for full size. (Compared to my ZD the image quality is not quite there yet. although I have not made intensive tests) The new id mkiv also has 12mp x1.3. Had a look at the 7d and was not totally convinced. My bet is that a new 2000?d or whatever with 12mp and the latest canon technology will be 'good enough'.
I think we are entering a period, like in the days of film, where there is a lot of different cameras for different applications. In my case, the ZD with shift lens & tripod for slower contemplative personal work(in B&W). The 450d for packshots, PR etc work where the ultimate quality is not necessary. 5d for the bulk of professional work, high iso needs etc. G9 works nice as a carry anywhere. Works well when travelling, people dont notice it and, at 80iso quality is nice for big prints.
So even if the price difference is small, as a second and back up camera I would rather have a 450d than a 50d.....
Regards, Ivan