Building Facebook apps can be dodgy business since there's no way to test without affecting your public profile. Of course, we can hack around this by creating test profiles, but even better would be a staging area for testing without being exposed to the outside world at all.
Right now, the only metric for "success" for a Facebook app is number of installs. I'd love to see some other ways to understand which apps Facebook customers actually value -- like, say, time spent using the app per session, or over a period of time.
Anybody else have any ideas about what would make for a good Facebook app metric?