Answers.com, the NASDAQ listed for profit website that makes heavy use of Wikipedia content has been blocked by China’s Net Nanny. Wikipedia has been blocked since November last year, after a brief period of being accessible. It seems that the new block was implemented to ensure Wikipedia content is not available at alternative URLs.
UPDATE: Answers.com is no longer blocked in Beijing (May 28, 23:11, news about block originally posted at 11:53).
UPDATE 2: May 29 — In the comments section readers in Beijing and Shanghai are saying that they cannot access Answers.com.