I generally like to limp in with medium pocket pairs unless I'm sitting in an unraised pot late.

I look at these like straight draws... you gotta hit the flop or get out, thus it's best to do it cheap.

However, if you raise late with these, and a rag board comes, you're sitting with an overpair and a preflop raise, and can generally steal the pot right there, or gain a few extra bets to your overpair.