That's a good question. I think we'll eventually see useful apps take off on social sites. The viral features of the Facebook API, namely integrating with the News Feed, have only been available since around March.

I think the ratio of useful to frivolous users of the Facebook API was much better before the new features came out. Before, the only useful thing you could do was pull down people's friend relationships from Facebook. This alone was extremely useful if you were already building something that had some substance to it.

Now, most of the apps you see are from people who are trying to capitalize on the viral featues of the API to sell ads. Instead of apps being valued for their utility, they're valued for their ability to convince users to invite all of their friends.

Eventually, the hype will die down, and some of the useful applications of the Facebook API will begin to become more prominent. Even now, I only get invitations to sill apps like Vampires and Zombies from one or two of my friends. As Facebook users begin to show more ability to discriminate based on quality, we'll see more people take advantage of the freely accessible social graph to actually do cool things.