I have a MacBookAir4,2.
If I'm on a Skype call in OS X, the mic works great.
If I'm on a Skype call in Ubuntu 12.10, I have to shout for other people to even hear me; it's very faint.
I also tried Google+ Hangout and it's the same problem.
I've played with pavucontrol and alsamixer to no avail.
Any other suggestions?