If you have installed the Google Voice & Video plugin for Gmail Video Chat then this will cause iSight to not work with Chatroulette, you will need to uninstall it with the help of GoogleVoiceAndVideoUninstaller.app that should be in your hard drive's Library/Application Support/Google/ folder. (NOT your home folder LIBRARY)
In Mac ...Finder ..click Macintosh Hard Disk ...and choose Library/Application Support/Google to find GoogleVoiceAndVideoUninstaller.app
IF this doesn't work ...then update your Flash version ..try the latest one (beta)
Clicking this link will download the beta version .... http://tinyurl.com/2frejs4