from a video standpoint:
t2i upscales from about 700 lines of resolution, gh2 is true 1080p
t2i is a 1.6x crop, gh2 is a 2x (theres a debate about it being 1.86x because of the oversize sensor etc.)
t2i is ef mount, takes a decent amount of lenses
gh2 is m43, can take almost any lens, including pl mount and b4 as well as leica m
t2i has an optical viewfinder, gh2 has an evf (so it works during video, but many prefer optical for stills)
t2i is manual focus only (but you can set the focus with AF), gh2 has usable autofocus with native lenses (which are amazingly sharp, but only focus by wire), but many people use manual focus
t2i has magic lantern, adds some very useful features (i'm not 100% sure on all of them, so I won't get into specifics). gh2 has been hacked to provide abc-intra at over 200mbps (though compression is being improved, and variable bitrate features are emerging). gh2 also allows iso up to 12,800 in video mode (only really usable in black and white), and there are a few other things.
t2i i believe has zebras or something to help with exposure through magic lantern, gh2 has a setting where overexposed areas will flash on the screen
t2i has a 12 minute recording limit, gh2 can record well over 30 min with the right patch/card
gh2 has a crop mode, a flip out screen, much less moire, slightly less rolling shutter, and the kit lens is made for video (14-140). t2i is cheaper
gh2 is a little smaller, neither are weather sealed, though i haven't heard of any issues with either short of full submergence
thats all I can think of off the top of my head, I'm sure I probably left a few things out