Well my upgrade path was 300D>30D>40D
I bought a 300D when they first come out, it was the first move to digital with SLR, I did not use it that often, over its life i had it, was great though for what I did use it, but when I got more interested in shooting football matches, 300D certainly had some flaws, so moved to 30D, 3 months ago, great camera, but moved to the 40D as I read it had better AF, tracking and a brighter view finder, for a good price, and it does on all those accounts.
I will prob get a Mk 3 eventually for the same reasons football, and sports in general.