Google Video is meant to be used inline--streamed, not downloaded. But with no playlisting features, one-off streaming is a little retro. Jkinberg at Sandbox Films has written a Firefox extension that rips the videos off the sites and puts them on your hard drive. (Another script is available for downloading YouTube videos.) It's doubtful that this thing will work in the upcoming Google Video Marketplace (if Google ever launches it), and I wonder whether Google will allow this script to continue existing, regardless of the company's friendly relationship with Mozilla and Firefox.