I´ve performed keying quite well a couple of times with standard miniDV-equipment. (nothing counts as much as lightning, as stated above a few times) I Used the Canon MV900 and XL2 for recording, streamed video at 720×576 (in Europe), imported the footage into an AE composition defined at HDV-resolution (1440×1080, again, in Europe), scaled the thing and ended up with a composition performing quite well on a sub-standard laptop, on the run. Mind you, this laptop did not render any of the final editions. But it works impressively, and it´s cheap.
Angry Arts