If you are one of the few users having trouble with the iSight scanning feature, check out the most recent beta version for the Pedias and let us know how the scanning goes. Conor has been working on improving it, especially for the later iMacs, and would like to hear your feedback. You'll find our email on the Support page.
(If the scanning still doesn't work for you, please check your console log for are any messages from the Pedias. These will include more information about the camera and product ID to help us out. You can access the console log via the application 'Console', located inside your Applications/Utilities. The newer messages are towards the end of the log.)