Yes, Youtube was blocked because of Tibet

According to several media reports, Xinhua has come out and said that separatists and supporters of the Dalai Lama had "fabricated" a video showing Chinese police officers brutally beating Tibetans after last year's riots. Though Xinhua didn't explicitly state the video, it's probably this one. Google has said it doesn't know the reason for the block, but "We are looking into it and working to ensure that the service is restored as soon as possible." So... we guess we won't be getting the 'tube back until either Youtube takes down the videos or Google finds some way to filter specific content from China IPs. Great.