After reading the article here on HN, "How fab.com gained 20,000 pre-launch signups in 10 days" I was inspired to use some of those elements in our facebook app launch and also add some prizes to the pre-launch process.
http://apps.facebook.com/gamesandprizes/user/profile/id/642840732/?srid=642840732
It still may be a little buggy but I would love to hear feedback (the good and the bad). I would be happy to share data on just how viral this goes down the road if anyone cares to know.