As the title says, FB is not for everybody IMO. The recent set of 1-star ratings list pretty much all the things that made me leave: questionable work-life-balance, no planning/structure, arrogant/ignorant coworkers, every man for himself/every woman for herself, cliques, political, inept managers, poor communication/rumor mill/back-stabbing, no teamwork, management by attention-deficit disorder.
The work-life-balance issue goes beyond the mere hours: it is expected that you become FB friends with all your coworkers, managers, etc. FB makes it impossible for the realm of your private life to remain separate from your workplace and coworkers. This wasn't working for me, but I recognize that for others this isn't an issue.
It seemed to me that much that is broken at FB is perpetuated by the in-clique and in fact gets sold as the great achievements of FB's unique culture.