Hello crotherman,
Have you tried using another Account or creating one in System Preferences, then testing Photo Booth, or Yahoo? Or even iChat?
If you launch iChat and open iChat Preferences, then click on the Video Tab ... what do you see? What about if you launch Photo Booth ... do you receive any error message?
Can you start the camera through the Accounts pref pane, by clicking on the Picture tab?
Click on the Blue Apple icon
in the menubar and select
"About This Mac", then click on the
"More Info" button, do you see the iSight Camera listed under:
Hardware ~> USB ~> USB High-Speed Bus
Can you think of anything you may have been doing just prior to this issue that may or may not be related?
Here is a doc from the Apple website:
How to Troubleshoot iSight
You could also try booting in
Safe Mode, then restarting normally again to see if this has any positive effect.