The biggest downside of the new 1000D to me is the focusing system. It sounds basically like what was used in the 300D and 350D - which is okay, but far from great.
I think most of that has to do with the number of cross-type AF points there are. I think the 400D, 450D, and (probably) the 1000D likely have a single cross-type AF point at the centre, while the rest aren't. Anyway, I don't know whether a 450D will have significantly better focusing than a 1000D. If you want good focusing, you'd have to get a 40D, I think.