Most 3D scanners use a digital video camera to capture data. Typical video capture rate is 5-30 frames per second depending on the camera, image resolutions, etc.
My current setup takes 12 camera frames to capture an image. I can capture a 3D surface in a little less than a second. It's plenty fast for faces and full body capture, assuming the subject stays still. It isn't fast enough for motion capture, however.
There are structured light scanners that capture in 3 frames (see Three Phase scanners) and Artec appears to have a scanner that captures in one frame and is capable of real time motion. I would love to get my hands on one of those, but I don't really have the need for real time scanning.
-Dan
Bluegalaxy Design
www.bluegalaxydesign.com