- viewfinders and autofocus stop working in video mode (and if you buy a T4i to get video autofocus, Canon autofocus motors are noisy and will ruin your soundtrack)
- has a 12 minute video clip length limit
- is susceptible to a phemomenon called moire when shooting brickwork, shingled roofs, patterned fabrics and similar subjects with fine details - as seen
here and
here
The GH2's viewfinder and autofocus continue to work in video mode, it has no shot length limit, the autofocus motors on most of its lenses are absolutely silent, and it is resistant to shot-ruining moire.
Take a look at the videos in
this post to see the quality of the images the GH2 can produce.
All of that said, Canon shooters work around these limitations and produce some absolutely terrific work. But people shoud buy these cameras with their eyes open. I don't want anyone else to be as surprised as I was when I tried to shoot video with the T2i