MacBook Air 2013 ExteMic Input Problem and Fix
First off, I am loving my MacBook Air 2013, just an outstanding computer, especially coming from a 2008 MBP. Anyway, here is the issue that I believe at least a few of you have had or noticed. When using any third-party headphones with an inline microphone, the Macbook Air for some reason does not pic up the sound properly, and the user on the other end of the call cannot hear you (this happens in Skype, FaceTime, etc.) it is a software issue, not hardware. When you go into System Preferences, under sound, when headphones are not plugged in, you will notice that there is an option for "ambient noise reduction", but once a pair of 3rd party headphones are plugged in this option vanishes.
So how to fix it, well aside from waiting for this issue to pick-up steam for apple to notice and send out a patch, fear not there is a temporary fix! When plugging in your headphones, hold down one of the volume keys on the volume controls built into the headphones, and hold it until they are plugged in. You will notice the "ambient noise reduction" box is still present and the headphone mic works!
The trade-off is the volume controls built into the headphones no longer will work, until you unplug the headphones and plug them back in. Anyway hope this helps! I can't take credit for this fix, I found it searching vehemently for a solution to this annoying problem, because I skype daily. I hope this helps those out there having this issue!