I can hear the person on the other side, but they can't hear me. In System Prefs, the blue bar reacts when I clap, but the same bar in Skype Audio/Video settings doesn't react. I've had this problem using Cisco WebEx as well.
In System Prefs, I selected Internal Microphone and the input volume level is up, so that can't be it. I recently upgraded to OS X 10.6.8, and I think (not sure) it didn't used to happen before that (could be coincidence, but I thought I'd share).
I'm on a MacBook2,1.
Hope you can help :)