but isnt this another argument against the 50D? if its images will start to look softer after f8, then youve got a very small usable range of sharp f stops. what if you need a really large DOF, or want slower shutter speeds??
The image will start to look soft at 100%. The actual point at which the image starts to look soft depends on how you're viewing the image. The higher the resolution, the higher the "magnification" of the image when you're viewing it at 100%, and thus the lower the f-stop required before you see diffraction effects.
The 50D has sRAW1 which, at 7.1 megapixels, wouldn't show diffraction until f/11.
Crop cameras in general will show diffraction effects sooner than full-frame cameras when you view their images at 100%, at least until recently. The 5DmkII will show diffraction effects at f/11 because its pixel density is identical to that of the 8 megapixel 30D. But whether or not you'll see it in a print depends on how large you print and how close you look at the print.