I've spent some time debating with libertarians online, and I think I've taken those debates as far as I was interested in taking them. Like communism, libertarianism seems to rely on an unrealistic model of human behavior. We're not all rational all the time, and most of us are not interested in striving to be perfect consumers. Most of us have better things to do with our time and little gray cells. That's why libertarianism is unworkable.
I think this observation leads us to the true connection between Ayn Rand's objectivism and libertarianism. Objectivism demands that its adherents be ideally rational and be more perfect consumers. The goal of objectivism is to instill in its adherents personal traits that happen to be necessary for them to live under a libertarian political system.