The object of the game, for any one of these ultimately temporary social networks, is to create the illusion that it is different, permanent, invincible and too big to fail. And to be sure, Facebook has gone about as far as any of them has at creating that illusion.

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Yet social media is itself as temporary as any social gathering, nightclub or party. It's the people that matter, not the venue. So when the trend leaders of one social niche or another decide the place everyone is socializing has lost its luster or, more important, its exclusivity, they move on to the next one, taking their followers with them. (Facebook's successor will no doubt provide an easy "migration utility" through which you can bring all your so-called friends with you, if you even want to.)