Thanks to Tannin for that splendid post - clear and informative.
Just a (newcomer) query though. Extrapolating from the figures given, my 18MP 7D would give a 7.15MP picture compard with the 3.3 MP from the much more expensive, full frame 1Ds 111.
I assume that you can't just deduce from this that the 7D is twice as good as the 1D for bird photography so where do the APS-C cameras lose out compared to full frame cameras?