I almost NEVER slowplay a set. There's a lot of reasons you shouldn't. First, you almost certainly will get called with a decent bet by someone with top pair (or even raised with 2 pair!). Second, why give someone a free card for a flush or straight? Third, and most important: remember, you want to BUILD the pot postflop when you have a great hand, and you WANT people to call you when they're way behind. Don't miss the oppurtunity.