I'm not going to but there is one rational reason why a libertarian would vote Democrat, to tye up the government. I loved it when the republican congress and clinton were bickering all the time, even excluding the War on Terror budget needs, government spending during the 90's were lower then today.
BOTH democrats and republicans are parties of big spending. Coming from a libertarian standpoint, if they're isn't a party to reduce the size of government then we might as well tie the current one up to prevent it from getting even larger.
The two issues that prevent me from taking that standpoint are the war which needs effective leadership and judicial confirmations. I'm pro-abortion but I'll put that on the sideline to get Kelo overturned.
I'd say that we see pretty much eye-to-eye on the issues, but the idea of tying up the government by creating inter-party gridlock is not a good long-term solution.
We need to kill off the party - root and branch - that is ideologically wed to big goverment and wealth transfer - and that's the Democrats.
Freed from the perceived need to compete with the Democrats for pig votes, the Republicans would come home to the underlying ideology - small government and individual responsibility. I'm afraid that has little chance of happening as long as the Republicans don't see a way to put together a majority without a certain portion of the pig vote.