I'm reminded of Mike Caro's misery index. The odds of you getting to the flop with nothing to make your set and at least one overcard are something like 75% for 99 (totally from memory).

That said, three limpers in front of you makes you 25% of the pot, so maybe that's not so bad. Like the previous poster said, it'll be hard to put you on the set if you get it.

Other question - how tight are the three limpers? If you raise it big, and one guys follows along, you're likely to be in that classic race of pair vs. two overcards - which again might not be terrible...

-dunk