Don't be too quick to blame this on political fear - China probably just wants to increase productivity in the workplace. Next on the chopping block.. Facebook, Digg, and Reddit.
There's a lot of precedent for this, too. The government blocked the whole iTunes store when a music single with the word "Tibet" in it hit the front page. They frequently ban news sites whenever news from Tibet (especially negative news) hits. It doesn't last forever, though. After things simmer down, they'll usually lift the general block and just keep targeted blocks on specific stories or pages.
I'm hoping YouTube comes back soon. Sometimes domains that were totally banned spontaneously become free and clear. Any blogs hosted by Wordpress were blocked until this last week. Now, no problem. Same thing with Andrew Sullivan's blog, and half a dozen other sites. I think it's just to keep people guessing.
IMO, if they're doing that, it's a very smart system of reducing dissent. I completely disagree with it, but then I grew up in a western country. I'm also not too ignorant to call China evil for doing so, they've made colossal strides in the past 50 years and perhaps in the long run this will be good for the country as a whole, potentially the worst thing that could happen is a civil war involving 1.3 billion people.