In my experience it's difficult to determine exactly what a libertarian is. I have friends who call themselves libertarians and some of them seem to me to be pretty much nothing more than free market Republicans. Others are a little more radical and want to basically eradicate government entities other than military and law enforcement completely. No environmental regulation, no public education, no Social Security, nothing beyond defense and protection. Still others mix a healthy dose of religion into it all. And each of these groups claims the other groups aren't truly libertarian. Looking over the responses to this questions in the postings here I have to say I'm impressed by several of them. There are some very thoughtful answers on this thread.
What often strikes me about my libertarian friends, those that think of their philosophy as a workable system rather than a label that sounds rebellious, what strikes me is the amount of common ground I, an unapologetic liberal, and my libertarian buddies share. We were all deeply alarmed by the Patriot Act. Civil liberties is an area where we seem to see pretty much eye to eye. We are also supportive of small businesses and view the rapid consolidation of enterprises into monopolies as contrary to the whole idea of a 'free market'. Most of these libertarians I'm discussing here are pro-choice, support gay rights and believe any kind of discrimination is contrary to their worldview.
Where I have 'reservations' about the libertarian outlook, again I'm talking about those who advocate a workable system, is, predictably, in the area of the role of government. It is often claimed that we liberals want more government. It is said we love government. Well, I actually don't care how big it is I just want it to be better at representing the interests of the majority without disregard to the interests of the minority. Currently, I don't love the government. I think it's been bought by corporate interests. And I blame both parties for this, more so the Republicans yes, but Democrats have pissed me off too. My libertarian friends often put forward the notion that bureaucracy kills every benefit government can bestow. The problem for me here is that every collective human effort creates a bureaucracy to some degree. Yes, they do get corrupted and lose sight of their initial mission. This happens to every single collective effort ever created: unions, corporations, governments, churches and charities. But I don't think the answer is to just chuck 'em. What's required is course-correction from time to time. I will say that criticism of bureaucracies is needed, and sensible libertarian voices are needed to supply that criticism.
I think the future of political argument, and I've posted this on previous occasions, will be about how we mix socialism and capitalism in modern society. Both of these concepts are part of every successful state system in the world today. And we liberals will debate with libertarians about the balance between the two. Both voices need to be heard and success will likely be achieved through compromise.