I presume that Second Life was created to make money rather than to address metaphysical philosophy, but I think Milan Kundera's famous book is based on the pain of not having another life in which the consequences of our decisions can be played out. But he wrote it before we had the internet!
OK, so Facebook is not a Second Life. But neither is it really integral to my First Life. Some people who are very closest to me are not here. And I can't imagine keeping this place updated with my status daily or weekly, let alone hourly. Yes, it is a great way to keep in touch with friends. But it is still a little like a wall to keep yourself in, as well as to reach yourself out.
Obviously I'm not talking about bricks and mortar. From 1979 I used to think a wall was a barrier behind which you could stay comfortably numb from the cruel world outside. Now a wall is just a convenient place for everybody to write their graffiti. That's fine .. go ahead :)