Why? It seems like nobody knows right now. We can't think of any particularly pressing anniversaries - the type of thing that has warranted a Youtube block in the past. Our best guess is that this might have something to do with the recent unrest in Tibet? It's not too out there to think that someone might have loaded a couple Chinese censor angering vids of the allegedly hundreds-strong protest.
Is this possibly because the US Navy posted videos of Chinese harassment in the South China Sea?
Also, the censors seem to have finally caught up with my favorite proxy, Outlaw Proxy (www.outlawproxy.com). This is what comes up when you type in the URL.