Hmm. It was eerily reminiscent of some of the Internet events I went to 15 years ago.
People are having lots of ideas, but many of them are ideas that have been had before, except that whereas before they were for the Internet, this time they're for Facebook. Now although the first time round we could afford to be idealistic about things, this time round we should be able to foresee the same problems we had before and do something about it.
For example, one of the things you get when you set up a Facebook application is an easy-to-use Facebook URL of the form apps.facebook.com/yourapplication. OK, so there's my first revenue model right there: cyber-squatting. You want to launch a product called Xyzzy? Well, I guess I could be persuaded to relinquish the slot...
Facebook's excitement with its "Like" button is similarly reminiscent of all the early reputation systems we saw, and possibly just as gameable. I'm not persuaded that an enterprising web site host couldn't either send Like requests from your browser whether you liked it or not, or obscure the Like button behind something else that you might want to click on (such as a Submit button). They could certainly hold you to ransom, making you click the Like button or they won't let you leave their web page except by killing the browser process (although thankfully, such browser-hijacking is rare nowadays as the perpetrators found it to be counter-productive).
There are new Facebook developments in meta-data, too, for use with the Facebook Graph system. The idea here is that web sites can tag their content so it's correctly stored in users' Facebook profile information. For example, news sites will say they're news sites so that when you Like a story on them it won't last in your feed forever; movie sites will tag their movie pages so that when you say you like them, they hang around in the Movie category indefinitely. Oh yes, and spam sites will lure you into clicking Like for something mildly amusing, but will have loaded their meta-data tags with advertisement data that will be forever in your Facebook profile unless you set your dogs on it.
Following this Internet-within-an-Internet theme, we could eventually see a Facebook-within-Facebook. The high-ups who were presenting kept talking about what their friends liked and what their friends might want to see, but they studiously avoided the fundamental problem Facebook has with friends: those people you tag as friends aren't actually all your friends. Some are, but others are business acquaintances, family, players of random games, people you met at parties, former schoolmates you want to snoop on and oops-I-clicked-accept cases of mistaken identity. Personally, I really want to be able to partition my friends into groups that I myself can create and name, and give them access only to friends in those same groups. Facebook, for some unfathomable reason, can't or won't do that; an app, however, could. If people switched to using the app, with Facebook acting as little more than a server, then we'd have gone full circle.
Still, there's plenty of opportunity to make pots of money here. Just think of something the Internet did first time round, then do it again except for Facebook.