Not having a T2i yet, I ask ignorantly- is shooting with "movie crop mode" the same as shooting in HD and then cropping out a 640x480 image, essentially? Or is the resolution actually better if you shoot natively?

The crop mode is suppose to be a 7x crop, which is much more than just a 640x480 crop out of a 1920x1080 image. It sounds like a 100% crop.