They're migrating to facebook. Social networks don't make sense if they're nation limited, be it de facto or by design. People will migrate to the biggest most popular one eventually. I suspect facebook is just the best (by some people's standards) social network and social networking eventually falls into a natural monopoly.
If Facebook were de-blocked today, you might very well see a mass migration. All my students (Chinese high schoolers and college transfers) going abroad immediately send me friend requests as soon as they get out from behind the Great Firewall.
