I love my 40D. And I'm not considering FF in the forseeable future.
First is price. I don't want to carry something that I can't afford to lose or break. Camera do get lost and broken a lot. And I don't think 1 camera is enough. I take 2 bodys with me.
Second, I love the speed and responsiveness of APS-C cameras. 5D is slow. 1Ds is not very speedy too. D700 is slower than D300. D3 and 1D is good, but they are just out of my range.
Last, I never find the PQ and high-ISO of APS-C cameras to be less than satisfiable. FFs are better, but is APS-Cs not good enough? I don't think so.
Again, if I become a pro or win a lottery, I may buy some D3s or 1Ds. They are really nice cameras.
EOS 40D+BG-EN3/350D/17-40 f4L/70-200 f4L IS/50 f1.8/18-55 f5.6/MacBook&ThinkPad