Cato actually has done some studies on the libertarian vote. It went overwhelmingly for George Bush in 2000, but swung about 20 points democratic in 2004. I'm not sure that they've updated the study for 2008, but my gut (and surveys of self-identified well-known libertarians) tell me Obama won the vote.

If you like market economics, don't care if your neighbor is gay, and don't feel like occupying countries on the other side of the world, there is really nobody pandering to you. You tend to move around.

Edit: Here's the paper comparing the 2000 and 2004 elections that I mentioned

http://www.cato.org/pub_display.php?pub_id=6715

Kerry did 18% better than Gore among libertarian voters, despite not having a libertarian bone in his body. Bush won the demographic in both elections, but lost 13% between 2000 and 2004, for a 31 point net swing.