Here are some more links for those interested in further reading.
The best is from TechCrunch, where the ex-COO of PayPal talks about the upcoming primacy of social networks in the spread of content. (He says the spread of power in terms of content referrals online went thusly: step 1, the portal; step 2, search; step 3, social networks and recommendations from others like you, personalized by people who like the same things you do.)
The second is a fascinating paper from Danah Boyd about American class divisions as viewed through the prism of social networks, ie most preppy, college-bound American kids choose Facebook; myspace is for rebels and/or kids who plan on leaving high school for the Army or a career right out of school, etc. I’m not judging, I’m just summing up.
Finally, Rex Sorgatz over at Fimoculous.com points to a Web page that aggregates the most popular Facebook apps on any given day… so you can quickly see what’s resonating with an audience.