Basic 7D video ?s

I have only tried out the video capabilities on my 7D once, just now. Reading the instruction book brings up some basic questions: You are limited to 4 min clips no matter what size video and card? How are the stills from video? Do they at all compare to the same size pix shot as a still? I see many comment on keeping the shutter speed at twice the frame rate. Price you pay is what for going lower and higher?

...4gigabytes no matter what resolution of video and card.

The video is made up of approximately 30frames per second and the max resolution is 1920x1080, approximately 2mega-pixel.

The shutter explanation