I've been working on such a thing, too but stopped it for several reasons. I hope you provide (without scamming people
) what I had in mind, so here was my feature set:
* Send coins to facebook friends
* without fees
* even dust down to 1 Satoshi
* allow to send to all friends with a timeout (if coins don't get collected aka. the friend does not use your app), they return to your balance within a week)
* outbound transactions would of course cost the normal fees
Reasons I did not continue this was that I did not get positive response here on the forum and considered you - the forum members - the first wave of people to spread coins on facebook. Secondly I was pretty sure Facebook would find a reason to ban this app very quickly. Thirdly I did not feel too confident taking a long time responsibility for your coins.
If Facebook allows this app to survive some weeks, I am sure it will reach millions of users.
Actually my app works in that it can receive coins to facebook users and send in and outbound but it is ugly, therefore please go for it!
For me it was a great lesson on how easy it is to prototype such an app with all the book-keeping already in place within bitcoind.