NETRESEC took a closer look at the long lasting DDoS attacks on github.com. One of the few instances of this type of attack that even made it to mainstream media.
The article finds random web browsers from outside China are tricked into reloading two particular pages on github.com. Apparently, this happens by manipulating requests coming from users physically outside China to services in country hosted content at the border infrastructure.
This is another example of why encryption is a good thing. General usage of SSL/TLS will prevent passive filtering infrastructure from manipulating traffic, and prevent such problems.