After 10 days, CSDN is finally back online. The official explanation they offered for the outage:
A newly registered user had posted on his/her blog many links to download Olympics-related videos from P2P sites - because we did not remove this forbidden content quickly enough, CSDN was inadvertently shut down for 10 days. We sincerely apologize for any inconvenience caused. In order for us to provide you the best possible service, please do not post pirated Olympic content here in the future.
Wow one errant blogger can shut down such a high-profile site (FWIW CSDN has an Alexa traffic rank of 768).. go figure.
Lesson: the Chinese government has firm control over the Internet in China, be prepared to face the consequences if you do not understand the current national conditions and play by the current rules and regulations. Rules and regulations can be quite fluid in China; the present Olympics-related general paranoia and lockdown is just one example of the fast changing environment in this country. Also, human cen sors are almost definitely required for any user-generated content website in China.