A few datapoints from the Facebook App Exit Strategies panel at Snap Summit 2.0 - featuring Seth Goldstein, Jeremy Liew, Jeff Clavier, and Lee Lorenzen.
Seth Goldstein says that over the next ~24 months eCPMs for social networking pages (including apps) will go from ~$0.50 to ~$3 as big brand advertisers start getting - this will multiply the revenue numbers that FB Apps are pulling in - making for larger exits. Seth says that online advertising spend will grow 25% YoY in 2008 over 2007 - mostly by taking market share away from more traditional advertising.
Jeff Clavier says that FB app valuations are in the range of 2-3x revenues - in line with general technology valuations. I personally think that this is not so good for app developers because FB app monetization is at a pretty early/rudimentary stage. Remember that FB Platform launched only 9 months ago.
Jeremy Liew says that the largest FB app exit that he is aware of is single digit millions, about half cash, half stock.