I believe that the kbase article from apples support page that was linked is what onmyown meant when they said Been there done that. Meaning that if they have already tried that kbase they would have already tried resetting PRam and SMU. If its happening in all other programs that would use the isight. You could try a few things which you might have already tried.
1. Try a new user.. I know this seems like something that just wastes your time. BUT, if the isight works in a new user it limits what could be wrong with your system.
If the isight works in a new user then it is obviously not a problem with hardware.
In that case, you would wanna try removing your start-up items. (System Pref.s Users, Select your user name, hit login items on the top and uncheck them all) If that works you need to narrow down which login item caused it. Check them a couple at a time, trial and error to see which one it is and remove it from the list. If this is not the case then you may want to move into the preferences folders and try pulling .plists for either the isight and or the programs that use it.(careful this could cause issues with iphoto/imovie that it won't be able to find your library anymore)
If you have the same problem in your new user it is either your hardware or the OS.. Try the isight on someone elses computer and that will narrow down that option.
That should pretty much narrow down any troubleshooting steps you could take for the isight.. Take it into a store and have them work it if you can't find a friend that you can connect yours to.
Let me know how it goes and Good Luck.