Back in 2006/2007 when I was doing web development, I knew a few people at F5 and Zeus Technology (developers of application firewalls at the time), and they said The Great Firewall was using loads of F5 tech with deep packet inspection for all data.

I assume 9 years later (don't know what the modern tech for web stuff is these day, but I assume encryption plays a key part) they're doing just as intrusive inspection and filtering of data.