Upgrading Camera Tip
I currently have a Rebel XT. I feel if I get a second camera like the XTI, XSI, or even a 40D. It really doesn't give me much more "photographic" advantage compared to my XT. However, if I decide on a 5D, there is much more difference. Why?
1) 5 D is a full frame, so much better noise performance.
2) You get 1 stop more bokeh (background blur) with all you lenses. i.e. your F4 lenses give you and equivalent of F2.8 lenses on your crop frame camera and your F2.8 lenses are equivalent to your primes on your crop camera. Which is pretty cool. So not only your camera is upgraded but all your lenses are also.
3) one lens does double duty or two focal ranges. I.e. 17-40 is a standard zoom on your crop camera but and ultrawide on a full frame.
So consider these points when thinking about upgrading. I hope this helps with your upgrading.