While Facebook may be gaining on MySpace in the U.S., the overall picture for social networking sites doesn't look as good. MediaPost reports that the market share of U.S. visits to the social networking custom category has decreased 19% year-over-year, according to more data from Hitwise.

Social networking site interest may be peaking—we've seen several reports to this effect over the past six months. But the mobile side continues to see action, as companies fall over each other trying to figure out a) how to incorporate physical presence detection, and b) how to monetize it all. The latter, of course, is something that's proving elusive on the desktop side as well.