On the T2i, only the center AF point is cross-type, whereas on your 40D, all 9 AF points are cross-type. The 7D has 19 AF points, and all are cross-type. So if you are currently only using the center AF point anyways, the T2i might be fine. But if you are accustomed to using the outer AF points on a regular basis, you may be disappointed with the T2i's autofocus capabilities, especially in low light situations.
The other thing to consider is (and I really don't know the answer): If you are shooting weddings professionally, are consumer level cameras like the Rebels reliable enough day in and day out? As I understand it, the Rebels have a much lower shutter life expectancy than the 40/50D and 5/7D, so they might not be the best choice for high volume shooting.
Have you gone to the camera store and actually held the T2i in your hands? If you are used to the 40D, you might find it to be a little bit "small" and not as robust.
