GitHub blocked in China - Update
The project hosting site GitHub is currently inaccessible from China, cutting off the country's developers from the valuable resource. A ViewDNS.info check shows that the service cannot be looked up throughout China. The blocking is frustrating many Chinese developers who cannot access one of the world's major repositories of open source software. As the country's firewall controllers rarely give any information on why sites are blocked, it is suggested by some that github.com is being blocked because of a dispute over a train ticket booking plugin.
The blocking appears currently to be at a DNS lookup level; IP connections are not blocked but GitHub makes extensive use of host naming. GitHub released a statement to the media saying it was still investigating, "but it does appear that we’re at least being partly blocked by the Great Firewall of China. We’re looking into it, and will update with more information when we have it."
Update (23/01/13) - It appears that service has been restored in China. After a number of hours of intermittent connectivity, ViewDNS.info now shows that GitHub's DNS is resolving correctly. According to a comment on Hacker News, Chinese developers protested and it appears the government relented.