One example that is often cited is the so-called "deregulation" of energy markets.

There was not actually deregulation. The markets were still highly regulated, so the act of deregulating part of them threw the whole system out of whack and everyone wanted to reinstate regulation.

More on this, here:

http://www.world-nuclear.org/info/inf65.html

So a deregulation failing proved libertarianism right?

Libertarianism is like prayer. If it works, the religion is right. If it doesn't, you did something wrong and it's right.

Take the passage of Prop 8 in California -- libertarians do not think that marriage should be something that the state meddles in at all.

Examples abound. I just mentioned one deregulation example because such things are often touted as libertarian accomplishments when in fact markets are often still highly regulated and the deregulation was just a handout to one interest or another.