I 've been living off facebook apps since 2008. Upside: life free of commitments. Downside: Too much free time. Right now, i 'm doing a PhD course.
Background: I've been working for a couple of months on a Facebook Page app called FanBldr.com and I've found it fairly difficult to operate.. it's hard to get feedback from users, Facebook is always updating the platform, and I'm not even sure what percentage of my users will upgrade to paying once I drop the paywall bomb. I find traditional web app development easier to manage and operate in the long term.