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Villain showed down a pair of 2 [img]/images/graemlins/club.gif[/img] 2 [img]/images/graemlins/heart.gif[/img] to take the pot with a set of 2's. I guess I was lucky he did not 3 bet the turn or raise the river.

Thanks for the comments. I definitely should have raised pre flop, but I am not convinced that raising the flop is an error.

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Raising this flop with your gutshot/backdoor flush/overcard draw is not inherently bad or good. It really depends on the situation. In a small pot with no read on my opponents I will usually just call on the flop if I have the odds to continue and im not worried about a raise coming from behind me. In a large pot, I am much more inclined to raise this flop with no read, since getting a chance to see a free river is so valuable in a large pot that I believe it more than offsets the chances of a 3 bet or of someone betting the turn instead of checking to me.
In general, the more aggressive your opponents are the stronger your draws need to be to make this play(premium draws like flush draws and OESD) but the more passive your opponents are the more weaker your draw can be to pull off the free card play( hands like gutshots, middle pair/bottom pair, and just overcard draws)