Not to pimp my own entry, but I just submitted a post to HN about a 40 yr old company that makes $50-100MM/yr selling white label social network services. Interesting, but perhaps not extremely scalable (i.e., needs a sales force).
Almost no (current) social networks provide a service - they provide a distraction. And we're supposed to be surprised that they're having a hard time making money?
I'd say "entertainment" is a service. Although entertainment can be a distraction, it's a) not necessarily a distraction; b) a component of being entertainment. Purely (or at least mainly) being a distraction isn't a service. And it's hard to think of most "social networks" as much of anything more than a distraction.
Really, of the major social networks, I can't think of one that does anything that's not done better somewhere else. And, at least so far, no social networking site has combined those services in a synergistic way.
It's easy to make money if you're willing to set a price. The trouble for web-based distractions is that they're afraid the price will be too high and kill their traffic.
Weewar.com is a solid game, but it's still just a distraction. The way they're making money is by providing a "pro" version where you get access to more distractions: http://weewar.com/upgrade
That's because the social networks haven't opened up the floodgates yet, they're still in data collection mode. The real revenues come when they sell your data -- when Facebook tells Miller that you are a central person in your social network who just sent a message about Bud Light to a frat buddy -- that's when Miller sends you a special offer for your next party and when the real revenues for Facebook come.
Online advertising is growing massively. Social network advertising is growing dismally. Why so many people are still kicking the dead donkey?