This doesn't bode well for Facebook because a huge part of their growth strategy was in getting the exclusive college crowd, then growing that circle to the early adopters, then growing THAT circle to everybody else. Even if they never lose their core demographic (which is to say, the students that made facebook popular, which have almost certainly graduated by now) -- if the exclusive college crowd moves to somewhere else, even just for one of FB's core services, it's a very bad sign.
What FB wants, rather, what it needs, is for people to rely on it for everything. If portions of its service become decentralized elsewhere, and heaven help them if they're able to integrate with each other, then they lose the power they currently have, which is in being able to get a pretty clear picture of your social circle from visiting just one site.