The NYT asks the monetization question of social networking software, but misses half the point - my guess is that a fair number of these players are looking to be acquired for their user bases, not the amount of cashflow they can generate in susbcription fees. That's because a captive user base can be massively leveraged for cashflow by someone who can feed it, for example, an advertising system that works.
Of course, that also means that there will be a strong winner-take-all dynamic in this market - and the losers will have burned through a fair amount of cash. Will they be able to achieve other means of monetization? Only time will tell - and my guess is no, because as Google's AdSense gains more and more competition, the rents that can be captured will fall in value.