Too many good ideas on both sides (and the middle) to respond to all for right now. I'm really enjoying this thread.
According the DP Preview comparison,
Although the Rebel T2i offers a competent AF system, the Nikon D90's advanced autofocus technology provides the advantage including better low light autofocus capabilities and offering greater reliability in our real world comparison tests.
Any comments re: this from the people here?
What I meant by this is that most people buying this camera will not buy lenses sharp enough to take advantage of the high MP's, meaning that for most consumers, the cons of these sensors will outweigh the pros, without them knowing it. DP Preview calls it a marketing decision, and I don't disagree.
And according to the DP Preview tests, the T2i does not perform as well at high ISO as the D90. I do not know if this is due to the 18MP sensor, as the 18MP 7D holds up well in all respects to the 12MP D300s.
But the bigger issue for me is the T2i's 18MP sensor results in a substantially slower burst rate, less photos to fill the RAM buffer, and slower transfer of these photos into the "fast" 30MB/sec SDHC cards. (T2is burst rate is 3.7 frames per second (fps) with a buffer that will allow up to 6 RAW. Nikon D90 does 4.5 fps and up to 11 frames in RAW.)
For the record, I do not mind high MP sensors, and understand there are
plenty of uses for them. And the 7D handles bursts quite well on 90MB/sec CF cards
(I can't get over this video).
Regarding handling, both cameras make my left hand feel like it's being torqued counterclockwise, the D90 slightly less so. I guess the only way around this is a battery grip. Much more money than I wanted to spend on a consumer camera.