Making money with Facebook apps

This article from Time magazine:

Google's Art of War — With Facebook

Contains this paragraph: "Facebook rocked Google's world last summer when it opened up its network to software developers and invited them to launch tiny applications there. The apps (also known elsewhere as widgets and gadgets) were fun and allowed people to communicate better or just horse around. Because there was more to do there, people started joining Facebook in big numbers, to play Scrabulous, write on walls and fling stuff at each other. The population quickly surpassed 50 million users — and that, in turn, created a great and wonderful market for software developers to build even more apps. With minimal work, developers could write apps that, if successful, could make them money via advertising. The more people who installed their apps, the more money they made. (A friend in that business recently told me about guys who routinely haul in as much $25,000 a day while their apps are hot.)"