Had lunch with some people from FEE yesterday (http://www.fee.org/). These are some pretty hardcore libertarian types who are focused on free market economics and individual liberty. They were pulling for Romney simply because while they certainly sympathize with Johnson, they understand that Obama is so much of a horrible option that it is not time for a protest vote. The president of the organization told me himself- “We probably can’t take 4 more years of Obama, or the country is in too deep.” This was a realistic Libertarian.
Social lefties like those libertarians you mentioned, can vote against open borders and the left when the economic choice is so stark.
I think most libertarian types will not vote for Obammie, but since the idiot demonizing by many Repubs as well as the cheating of the RNC on Paul delegates and rules, they may not vote for Romney. Stupid RNC goes limp for Hispanics, Blacks and the mushy/leftist middle of the road voters but manage to run off natural allies like Libertarians and strong Conservatives. If the Repubs lose this election it is time to say FU Rove and the rest of you frauds!