One of the best features of the T2i, is its gorgeous 3 inch 1 million pixel LCD screen at the back. This is the best screen on any Canon camera, to date. Even better than the 1D IV, 5D II. Reviewing pictures or video taken on the screen is a real joy.
Traditionally, Canon used a very small jpeg (about 200k?) file embedded in the RAW file for playbacks. Basically, you are looking at a tiny picture, however many times you enlarge it. For this reason, checking critical focus was a huge problem, because you can not be sure what you are looking at is representative of what the picture is. As late as the 1D Mark III, it was still done this way.
The T2i, surprisingly, seems to use the full resolution of the pictures for review (or a much larger embedded jpeg). You can zoom all the way in, and won't see jagged edges or artifacts of the tiny jpeg that used to be. Only one minor complain -- the image displayed on the LCD seems much sharper than the real image. This is usually not an issue as you can always sharpen the picture later.
Once again, an updated and refined feature that adds really joy in use, to the T2i.