The U.S. Military has put blocks in place to prevent its users from accessing sites such as YouTube, eBay, Amazon, among others.
The block on such sites has nothing to do with content, however, as this was done for bandwidth control reasons. The U.S. Military decided to block the sites in order to free up bandwidth to better serve those using the network for Japanese recovery efforts.
A worker for the U.S. Army posted a commented on Gizmodo relaying the notice that he or she received about the blocks:
The person noted that, aside from Amazon and ESPN, most of those sites are normally blocked by the firewall.