I noticed recently that Photobooth on Apple computers is really the killer app - in terms of selling. I was trying to convince my parents about the benefits of a Macbook, and they didn't really understand the creative aspect until I fired that up - it really is a ton of fun, and everybody likes to take goofy pictures of themselves.

I think it would be great to clone it, or expand existing camera apps to do something similar.

For those not in the know, photobooth adds great and unique realtime effects to the built-in webcam.