I've got a logitech UVC compliant webcam which works perfectly (no OSX drivers needed) in 2.5.0.85, but doesn't work with the latest beta.
It's odd as the previous version to 2.5.0.85 didn't work either, then 2.5.0.85 sorted the problems, but 2.6 seems to have broken it again!
The camera appears in the list but when selected the light does not come on and there is no picture, not even a preview in the preferences window.
UVC support seems to have slipped back two versions, so it's back to 2.5.0.85 for me!