I was just in China a few days ago. Was there for 3 weeks prior to that. I have a VPN setup in my apartment back in the US and I typically dial in to it. It was great for the first two weeks and a half weeks. After that, it would fail to authenticate or work really slowly, randomly drop traffic, then disconnect after a minute. I was using a relatively insecure PPTP system with 128 bit encryption. I wasn't worried about getting spied on, I just wanted news, youtube, and social media unblocked.
Frustrated, I had a friend set up a PPTP link at his apartment, using different keys and a different IP. That worked perfectly for the last few days I was in the country. So they're definitely doing some kind of long-term traffic analysis over many days, and then blocking close to real time after that (30-60 seconds).
Basically I got to witness the blockage go into effect. Yes it's real. Yes it's general purpose, not a high level block on specific free websites. Yes it was a huge pain the the ass.