The downside of the Captivator (as compared to the Quickcam) is that
you'll need to supply a video camera. You've also got to install a
board so you can't easily move your capture device from machine to machine
like you can with the quickcam.
The upside is that it has applications beyond cu-seeme (it can
capture in color (up to 24 bit color)) either stills or movies,
from a camera or vcr. I'd guess that it can capture larger images
than the Quickcam and can capture at a faster rate.
The bottom line is that if you've got a camcorder lying around the house
then there is a cheap, reliable, cu-seeme PC video solution available
right now.