Ecamm is producing a webcam exclusively for the Mac OS. And while it's certainly not a terrible product, it doesn't make much sense to me.
I mean, it's a decent camera. Nothing amazing, but for $150 bucks, it's respectable. 640×480 resolution, about 4 hours of battery life. Even comes with a min-tripod. Seems okay. I guess if your computer didn't come with a webcam, yeah — it might be something you'd think about buying. I guess it could be used as a possible nanny-cam or something like that, but otherwise I don't see much of a point. If you do want one, they'll be shipping at the end of March this year.