Maybe not capture, but you can write to the pins at least that quickly. I've seen projects that use the gpio of a raspberry pi to drive an FM transmitter at 100MHz.
Ah, my bad. I was actually thinking afterwards about how they could be doing the frequency shifts and what kind of sampling speed they would need for accurate, small frequency shift adjustments.
http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...