Originally posted by Liney One who start with a blanket ban on everything, and only permits access to sites if you apply for permission and justify why you need it. In my job I can't justify this site as a valid reference source.
I work for a DoD organization, and I'm a little surprised they don't do this. Some things are blocked like YouTube, but that's less for security and more for network bandwidth. I think they don't do it because a) they'd have to hire a bunch of people to vet and update the white list and you'd constantly be fighting with them about whether something is really work or personal, and b) it's a bit of a morale thing to allow people occasional personal web access at work.