There's not a single "right" way to play these hands. Against truly aware players, you should mix your bets up every now and then. That said, I do generally feel it's overly weak/passive to open limp with PP from early or mid position.

Also, you want to increase action w/ these hands. It's much easier to get paid off well if you hit your set with a raised pot than if everyone just limps around.

Finally, as Bair said, it's patently obvious you have a low/mid PP if you limp/call from early position. I've become very aware of this lately and have been able to avoid sets easily b/c of it. Martin's right, though, that there's probably about ten players at the lower levels paying enough attention for this to matter and four of them are posting on this thread.