I went to a Facebook developers’ hackathon last night at Thumbplay in New York. I wasn’t the invited participant. Son Jake was. I was merely the chauffeur. Nonetheless, it was a nonvirtual Facebook for me, for I found all sorts of friends there: developer colleague, show-biz pal, investment guy, political geek. Everybody’s into Facebook.

The excitement of having this easy, quick platform and built-in audience and new architecture of content and interaction was palpable. David Henderson of Social Media reminded the group that this has exploded in only 45 days. There have been 125 million app installations and it just keeps growing: more people, more apps. . . . and we haven’t even hit Labor Day and the return to school yet.

What we don’t know is the churn of these apps — only the net growth, not the number who drop off and are replaced. A lot of these apps have a half-life like show business, only accelerated: cool comes and cool goes. But others will become fundamental to this new social architecture. I don’t think the fundamental ones have been invented yet.

There was, of course, a lot of discussion about monetization, with one skeptic in the crowd drawing everyone else’s justification and inspiration regarding revenue: the discussion turned into a human wiki. There’s advertising, of course, and direct-response and barter and loyalty points systems and virtual currencies and also research. Henderson said that at the food fight app, users started with $10 to buy rotten tomatoes but wanted more and so they offered food fight currency in exchange for answering market research questions. To date, he said, they’ve received 20 million responses: 80,000 users per day, 25 per user. That’s what excites them all: instant scale.

There was, of course, much discussion of what Facebook allows and doesn’t allow and what’s behind every decision. Jake chuckled at all the Kremlinology that was going on. “They’re overthinking,” he said. Some things are done just because they’re done, no vast conspiracy.

What excites me most is the prospect of the pipe reversing: using Facebook to help organize the larger social infrastructure that is the web already. I’ve suggested to folks that they use Facebook’s real identity to feed real identity on their sites and forums. One participant said Facebook will plug into the social grid of the web. Or was that vice versa?