It's the run up to that all-important anniversary of the event that never really happened in China 20 years ago. I'm not surprised, and most others aren't either, that the government decided to "harmonize" a great many Web sites that could endanger the harmonious socialist society with Chinese characteristics. Those Web sites include Twitter, Flickr, Hotmail, Youtube, WordPress, Blogger, and the rest of the decent half of the Internet.
I won't get into the seemingly random Great Firewall that blocks harmless sites but leaves others with more detrimental information open (they still have some pornographic sites open). The more important question to ask about the Great Firewall is what does it really achieve? Does it preserve this harmonious society ideology?
The information that the Chinese government wants to hide from its citizens are those that include voices of dissent--human rights advocates, environmental activists, anti-corruption activists, and democratic reformers. Blocking information from such groups will keep much of the population in the dark, but most of those people wouldn't care about such information to begin with. Students who are indoctrinated in the CCP propaganda brush aside dissent without ever considering the purpose behind it. And the common Chinese citizen doesn't give much thought to politics.
Those involved in dissent are also not hurt by the Great Firewall--to them it's more of an inconvenience. There are plenty of ways around the blocks--VPNs and proxy servers. If they want information, they can get it. If they want to spread information, they will find a way.
The greatest problem for the government this time around is that they blocked access to Web sites that the common Chinese Internet user uses. There are many people there who use Twitter and Hotmail. To these people, it's more than an inconvenience. These people may not have cared about online censorship previously, but now it affects them. If anything, it can turn a politically apathetic person into a vocal critic. It's the small curbs that can do the most damage.