To say that Microsoft "won" is to be mired in zero-sum, winner-take-all thinking. If you can look at Apple Computer's earnings reports and see a company that has "lost", you're smoking something.
Microsoft is profitable, Apple is profitable. And the masses may outnumber the elite, but the elite has a lot more disposable income per capita.
There's no reason why both MySpace and FaceBook cannot "win" simultaneously.
I'm not saying Facebook is worth 15 billion (that'd be stupid...I'm talking Stave Ballmer level stupid), but one can't say they've lost to MySpace, when the market is still wide open worldwide, and Facebook seems to know how to execute internationally than MySpace.
But, I think Facebook will lose, in the end, to a few dozen companies that build a better garden without the walls. Each will be smaller than Facebook, but they'll end the reign of Facebook and MySpace with a wholly different process of social networking. (I think a single destination "social portal" is as doomed to failure as the whole web 1.0 "portal" idea turned out to be...portals will always be less interesting than the whole Internet, so when the whole Internet is socially enabled the social portals will falter. The oracle has spoken.)
Edit: actually, the MySpace numbers are out of date too, so if they've grown at the same rate, MySpace should still be 4x bigger.
And I agree that the future of social networking is probably something that hasn't been invented yet. The market is maybe 5 years old, which is about the same age as search when Google started kicking ass. My startup is actually in the running, so I've got a vested interest in FaceBook failing, but we've got so far to go that I don't even dare to hope...
I can kinda see FaceBook vs. MySpace as being today's Apple vs. Microsoft (or IBM) battle. FaceBook's cultivated a sort of elite brand - "we're better than Myspacers simply because we're on FaceBook". But remember that Microsoft eventually won: the masses, by definition, are far more numerous than the elite.