My overall impression: Perry did well enough, but he was surprisingly badly prepared for predictable questions about global warming and even his Texas record. He was confident and aggressive, but he lost altitude during the evening.
Romney was I think quite right to suggest that conservatives are not going to succeed in reforming Social Security if the public believes the effort reflects hostility to the program. I also think he was shrewd to resist the opportunity to take a justified, but not strategically important, shot at Perry over the HPV mandate. The primary encourages candidates to overstate differences and make one another sound like failures, and a candidate ought to be to make a case for himself over the others without being hyperbolic.
On the merits, I think Romney won. But he is now the underdog, and he did not win by enough to make a difference.