It would seem like good policy for a company built on the premise that everyone should share their information to actually share their information. I'm not saying that they don't have ideas and plans on how to proceed, I'm just saying that if they were really confident about the viability of those plans, they'd be more vocal about them.
As it is, my own guess is that facebook's business plan involves selling the personal information of its members. This would be the most obvious commodity and also the most obvious reason why facebook wouldn't want to talk about their business plans.