I think that things are going to be awful over the next four years, regardless of who wins the White House. Now I know some people (even staunch libertarians) are very passionately hoping for an Obama win, because they would rather a Marxist than a Mad Bomber.
I agree that in a perfect world, Obama would be much more peaceful than McCain. But of course, we don't live in a perfect world. And I have seen nothing to indicate that Obama will implement the peaceful policies that (I agree) he personally desires.
The most classic example is Obama saying something like, "North Korea, Iran...these are tiny countries that don't pose us any threat." Awesome. Somebody needed to say it. And yet, within a few days (maybe even just one, I can't remember) later, he completely reversed himself and said something like, "I have always said that Iran and North Korea pose serious threats to this country." So forget the blatant lie, it's rather that he is lying about something so crucial.
A more recent example concerns the "negotiating with rogue leaders" issue. Obama clearly said he would be willing to sit down with no preconditions with the leaders of "terrorist" states. Awesome. Somebody needed to say it. And yet, when Palin tried to embarrass Biden with that, what did Biden do? He lied about it, and said "Barack never said he'd sit down without preconditions..." or something like that.
I have been personally burned in this matter, so I am warning libertarian Obama supporters not to make the mirror-image mistake. Back in 2000, Bush was running against Al Gore, and I was terrified of a Gore presidency. I thought if he won, Gore would impose a carbon cap on US businesses, raise taxes on rich people, blah blah blah. I didn't think much about it, but yeah I probably would have conceded that Bush was more likely to blow up foreigners, but still, for me at that time, I thought Gore was the clear and present danger because of his socialist tendencies.
I think we see how ridiculous my worries were. (Note that I have NEVER voted for George W. Bush. I can't remember if I did vote in that election, but if I did, it was straight third-party down the line, either Libertarian or Constitution Party depending on who was available.)
It is a myth that Republicans are good on economics while Democrats are good on foreign policy. Nixon closed the gold window and instituted wage and price controls, while Truman nuked babies and LBJ bombed the crap out of Viet Nam.
Let me close with this final observation: If Obama wins and there is another terrorist attack on US soil, he is going to "have to" take aggressive action such that future libertarians will ruefully conclude, "Yeah, President Obama believed in diplomacy the way President Bush believed in free markets."