UTG limp bluff raise - how often?

[Frostie]

You know, when people are in early position, and they limp in, someone raises them ahead and they re-raise, representing a big pair (such as AA, KK, QQ). I know it's good to do when you feel they're weak. I do them rarely, however I usually do them with hands such as KJ, KQ, or AJ. I do them against people with same stack sizes and not very experienced. Any other good reads on when to do this?