The inbuilt iSight video camera wasn't working in Skype or PhotoBooth. In both cases it was giving an "No video camera detected" error message.Rummaging around turned up this note that confirms the console view that there's a missing QuickTime file. This is how to fix it:Close the relevant apps, then running the following (from a Terminal window) entering your account password if required:
cd /System/Library/QuickTime/QuickTimeUSBVDCDigitizer.component/Contents/MacOSsudo chmod 755 QuickTimeUSBVDCDigitizer
And relaunch the programs using the camera.