I think as always it depends on your opponents. If it is a loose passive game, I'd limp all day long and hunt for sets. Why raise if you are going to get 4 callers with your pocket 4's anyway? The implied odds of getting paid off by even top pair weak kicker when you hit a set in that type of game are usually pretty good. In that game, if I don't hit a set, I fold to any aggression. If I am playing against more skilled opponents, I'm popping it up if I'm first in the pot. If its late in a tourney, I'm popping as the first player in the pot. If I'm called, post flop I'm making a continuation bet. I think it totally depends on opponents and what you are playing (cash game vs. tourney and what stage of tourney).