I think one of the issues with Facebook Apps, and Facebook in general, is that too many apps are there "just for fun"--sure, people use them for a little while, and heck, they might even keep them on their profile after they ever click through to an application page (I think I have 4 or 5 apps installed, but never use any of them). They're all short-term proposals. Some of that I'm sure was the rush to get to Facebook first and build a user base quickly, but so few folks have actually focused on the "killer app" that provides a great deal of utility based on what Facebook offers through their APIs (which is a LOT of valuable data). Some also, I'm sure, is the fear that once you develop a truly useful app that people find value in, there's still the risk that Facebook will create their own bigger, better version (most recent example is IM). If you want to have lasting value as a Facebook app, you have to provide something valuable enough to drive traffic TO Facebook, not just THROUGH it, because while total pageviews and users are increasing, the initial fascination is starting to wear off and Facebook itself is become more of a tool (meaning everyone uses it, sometimes) and less of a cool new traffic-driving site that people spend hours playing on.