I just installed eyetv hybrid and after that I could not use my integrated iSight camera (in my Mac Book Pro) with Skype or iChat. They would simply say: No camera connected.
However, starting Photo Booth once fixed this issue. After starting Photo Boot (which showed that the iSight camera works) and just closing it Skype and iChat video worked again. I assume that the eyetv installation just disabled the existing video devices and forgot to insert them again and that Photo Booth does a better initialization than Skype or iChat.
Of course I assume a reboot would fix this as well, but who likes rebooting all the time. After all why do I have a Mac. :-)