Used to be a libertarian, then i started reading more and learning that capitalism is more nuanced than i had originally thought
Books like these really changed my world view:
http://www.amazon.com/Bad-Sama...&qid=1248965816&sr=8-1
(edit: note, the book is not anti-capitalist either, it advocates free trade is great for developed nations, but spotty or downright bad for developing nations)
I had an intellectually lazy notion that all economists were more or less rightwing and they 'proved' that the free markets worked 100% of the time while government intervention was doomed to failure all the time until i read that book. Apparently economists are not 100% trickle down economics free market fundamentalists. And you don't have to be in order to be pro-market either. For example, 81% of US economists are in favor progressive taxation.
libertarians today are like the communists of yesterday, it's a utopian ideology that works great in 'theory' but has lots of problems in the real world. You pretty much have to believe that everyone is a completely rational actor, there's no such thing as information asymmetry, and there are no such things as market failures to be a true libertarian or that while markets can sometimes fail, government intervention makes it worse.
Edit: also, contributions by economists like joe stiglitz on such ideas like information asymmetry really helped shape my view
Also, voted 'ron paul is an idiot', none of the other choices reflect me ('other' is too vague)