The primary reason I bought this camera was to try the HD video. I am embarrassed to say that I haven't done much with the T2i's video. I did record the swim meet of my kids last week, and I would like to share some experience. If you are expecting to see sample video, sorry. I haven't found any app that allows me to do video easily.
Let me just say that doing video with the T2i (or any DSLR) is not easy at all. It will take a lot of time and practice to get good at. The primary problem is auto focus, and the holding of the camera.
The T2i has auto focus in video mode, same as live view auto focus. For video work, it good as not having it. On average, achieving focus in live view or video takes a few seconds. It's much faster focusing by hand, and for this reason, choosing the right lens can make doing video easier.
For action video, a zoom lens is preferred, for that matter, a push-pull zoom lens is ideal. I tried the twist zoom lenses and it causes the zoom action to be very jerky. The best lens I have found for video is actually the 100-400mm f4.5-5.6L. This lens has adjustable friction for push-pull zoom action, and manually focusing is quite easy. The 70-200mm f2.8 is a bit harder to use.
For critical focusing during action, it's very hard to do. For swimming, I was able to manually adjust focus to follow the swimmer, and it didn't turn out too bad.
Another area that affects the video is how the camera is held. Holding it by hand is just asking for trouble. It's tough to hold the camera still, especially for telephoto. Using a tripod or even a monopod will help tremendously.
The T2i has manual exposure control, which is a real plus, as you can adjust ISO, aperture or shutter speed independently. However, for situations where lighting changes often, auto exposure works best.
Video quality -- for the short time I used it, I find that even at ISO 6400 the video looks quite nice. Anything below that, it's fantastic.
I think video with DSLR is best for movie making, where scenes are setup, you can pre-focus, and with fixed lighting, etc. So, don't chuck your video camera for your normal family video just yet!