Haven’t shot with a 1000D but have handled one and it feels a bit more plasticky than the 450D (which I own). The 450D has a bit more textured rubber on the body and a more robust lens mount.
Other than that I believe the major differences are:
– Two less autofocus points on the 1000D – I use the centre point 99% of the time so no big deal for me there.
– Two less megapixels on the 1000D – so what?
– No spot metering on the 1000D – I use this occasionally on the 450D and have found it useful for wildlife shots in poor lighting.
The 450D does feel better than the 1000D but, depending on the type of photography you will be doing, the different features may not make a huge difference. If I was buying all over again, I doubt I could really justify an extra £120 for the extra the 450D offers. Either camera can do far more than I can.