I'm currently an Air Force contractor and I recall it being blocked for a very brief period of time back around 1995 or so, then allowed to return without posting capabilities. Now, at least where I work, there are both reading and posting access. It's hard to see why they would block it now, given the wide-open access to YouTube and social networking sites.
Very interesting that a site that did not exist could be blocked.
Interesting, when I left in 2009 FreeRepublic.com was definitely a blocked site. And you may laugh at this one. NASA.GOV was also blocked. If you needed to go there you had to have a authorization given to you by Space Command and my own company.