Along with the 60D/600D decision comes the lens decision. I have a two lenses for my 350D - the 18-55 that came with it, and a Sigma 18-125, neither of which have IS. So I could get a new body and continue to use those lenses, or get a new lens with the new body, since the extra cost of a kit over the body only is half of what the lenses cost alone.
The 60D and 600D are available body only, or with 18-55 IS, or with 18-135 IS. The 60D is also available with 17-85 IS USM. Now the 17-85 IS USM costs as much, if not more that the 18-135: is it worth it? I'm not a frequent lens-changer; I prefer so-called 'super-zooms', but in this megapixel range, where further zooming can be done later on the PC, is there any reason to have a heavier super-zoom?
Which brings me back to the 60D vs. 600D debate: do either, or both, have digital zoom?