We often accept people who reapply. The best known is probably Drew Houston of Dropbox. There were at least two in the most recent batch: FanVibe and PagerDuty. For the PagerDuty guys it was the fourth time they'd applied.
When people reapply it's often with different teams. I think all 3 cases I mentioned did.
People do change somewhat between applications. Someone who's only 25 gets 4% more experience each year.
And also, as we say in the email when we turn people down, we're often simply wrong.
I'm actually curious now if we set the record for most rejections prior to an acceptance.