It seems, that at least in Beijing, it is not so easy anymore to extend your F-Visa. Until now, it was never a problem to extend it for another 6 month, now a few people I know had problems even getting a 3 month extension.

Probably, teh guidelines changed, because the Chinese government wants more control because of the Olympic Games next year or maybe more control over foreigner coming to China with an F-Visa and working here without a proper working permission.