At my company, interns rarely ever join back as a perm employee. At least not as an extension of their internship to a perm role. Even the interns know that so they just hang around trying to pass time till the internship is over. Ironically they hold the cards, so we have hardly any influence over them.
Contractors on the other hand are a different story. They all yearn to be get a permanent role and most will go to any lengths to please their bosses. And if the contractor is a hot girl, then the boss is a real lucky bastard
Had a case where this contractor and boss (married) always used to be on leave on the same days. She wasn't really that good at her job but after her contract got over, instead of renewing it, the boss got her a permanent role instead. That's when the gossip started and shortly after the boss left to another company. She was let go for poor performance later, but she got a salary boost and, for what its worth, a pedigree company name on her CV.