Fun fact #1: That's believed to be why the Chinese government orchestrated the attacks against github in April 2015 using the great firewall to distribute infected javascripts via Baidu. They were trying to force github to take two projects offline that were being used to get around the great firewall and gain access to the unedited NY times online. The Chinese government can't selectively block those projects because github enforces https sitewide.
* Fun fact # 2: An intermediary of China Internet Network Information Center (CNNIC) issued several fake certificates for Google-owned domains in March of 2015. Google untrusted the certificates in Chrome and Android and Mozilla did the same in Firefox.
https://www.ietf.org/mail-archive/web/perpass/current/msg019...
and that is one part of what the gfw does.
google 'how does the gfw work' if you want a broad overview. there was a really in-depth explanation on HN not that long ago. sadly, i'm unable to find it at the moment.
You could probably do it on on 0.1% of the NSA's yearly budget. (Which, after some Googling, turns out to be 10M USD. That's even more than I expected.)
The roaming packages of foreign mobile users also don't get filtered.
If you are a Chinese citizen you most likely will be filtered, I've been to China multiple times companies will usually have a dedicated work station with HK internet the rest will be filtered hotels usually also get internet through HK not sure if this is only for foreign guests or not, on normal internet connecions Wikipedia and the likes were definitely blocked at least as recently as February 2015(last time I visited main land China£
I agree that blocking the international internet is harmful to innovation and the economy, but the question of how harmful is largely based on how large the market is. In China's case, Baidu isn't as extensive as Google, Youku doesn't have the Khan Academy or a lot of other things YouTube does, but they're still huge and it's not that bad.
China's internet isn't as rich as that of the entire world, but it's still large and vibrant. For the Russian internet it's a bit worse. If a country the size of Denmark decided to only their own versions of fb, youtube, wikipedia, etc, it would be a catastrophic loss.
As a laowai, I'm beginning to feel more isolated. If it wasn't for the pollution, it would be the biggest problem in living here.