The New York Times magazine recently ran an interesting, extensive profile on Nicole Wong, the deputy general counsel of Google (and by extension, YouTube) and the important role she and her colleagues have in regulating how users engage these extremely popular sites: Google's Gatekeepers.
Basically, they're the censors. I imagine it's not an easy job, simply due to the sheer volume of videos posted to YouTube—an estimated 13 hours of content uploaded every minute—but also because the parameters of the vetting process, and the way people use YouTube, must be changing constantly.
*
