It happened with Geocities, Yahoo’s attempt to capitalise on primative personal website before the dot com boom. It happened when MySpace was acquired by NewsCorp and it happened when Bebo was sold. Not to mention what has happened to FriendFeed after its sale to Facebook.
That happening was failure. There has never been a decent takeover of a social network to my knowledge. Let me know if I’m wrong, but I really think a socialnetwork, but the time its been sold, its on the quick demise as its users flee.
Whether FBook will ever manage to float is anyone’s guess, but this could well be the peak value of the socialnetwork.