I have a macbook air 4,2 (13" - 2011). The isight camera has become rather erratic in quantal. If I just pull up something like skype and go into the settings, things look fine. The problem occurs when I am in an actual network video chat. The other party sees me skipping, lagging, still video for 30 seconds at a time, etc. Audio works without flaw during those times. Also, in OS X in the same applications (skype and google plus), on the same network, things appear just fine.
I don't have hard evidence, but IIRC, this problem did not occur in precise. I know that my video chat has worked in the past, and I believe that the quantal upgrade was the dividing line.
Is there some problem with the driver for the isight camera? Some kind of settings that I am missing?