According to a recent comScore report, social networking sites now account for more than 21.2 percent of all US online display advertisements. And out of that chunk, Facebook and MySpace account for more than 80%. On one hand it positively underlines that where people spend time, money will eventually follow. On the other hand, it also underlines the very high dominance of a few successful sites/services/communities grabbing an extraordinary high portion of the total revenue.