People keep saying facebook will disappear... but maybe it won't? Maybe it will become like email, less used but ever-present.
Surely in the future there will be a better way of differentiating ourselves than "john-doe.com", "johndoe.com", "jdoe.me", etc. And what happens when JohnDoe #1 and John Doe #2 are famous people? Who gets the "verified" badge on social networks? It isn't sustainable, and Facebook and others are bound to change this sooner or later.