Chances are good in 2012 that a majority of libertarians lean center-right and should favor Republicans.
Libertarians are a bit unpredictable. Leaning doesn’t mean pulling the lever.
From The Skeptical Libertarian, here is one view:
“A lot of people say that the Libertarian Party just works as a spoiler, because it can’t win. Well GOOD. That’s a valuable function: it penalizes the Republican Party for being anti-immigration, anti-gay, pro-war, and lousy on personal liberty. It shows that there’s a significant group of people who are fiscally responsible and are being alienated by the Republicans’ backward social priorities. That’s the kind of pressure we need to put on the GOP, since reforming it from within is evidently a failed project.”
“If it does nothing else but spoil the election for Romney, to me it will have served its purpose entirely.”