In a SNG, I'm willing to take a shot in the small blind with almost any 2 if a few conditions are met:
-3 or more limpers
-It'll cost me less than about 1/20 of my stack to call
-BB isn't one of those players that can't stand to let people limp and will probably raise.

I think this is a very profitable play ... it doesn't hit often, but tends to hit big, and the risk is low.

I won't play hands that I am likely to question where I am at even if I hit twice. For example ... 34o. If I hit 2 pair, I am easily counterfeited and if an Ace comes, could easily be beat. If I get a straight draw, someone else could easily have the top end.