On one side it is worth considering the potential for bringing staff, partners and customers into a social network together. Consider how your future state internal network will connect with the outside world. On the other, think about how you will connect your new internal system of engagement with existing systems of record (something Facebook is not designed to do).
Facebook might not be the ideal social enterprise platform, but with the right strategic conversations internally it is still a great metaphor to build on.
I quite often get critics because I do use the metaphor when explaining IBM Connections. Nevertheless I believe it is a great way of getting the conversation started.
(And - of course - I don't believe that a Facebook or a Google+ are made for usage within the Enterprise. The requirements are to different ... Compliance, security ... And an enterprise can never risk to give away or not own its own data.)
The really interesting question is how to use Facebook, Google+ or Twitter for communicating with customers and prospects, leverage the reach without loosing control over the data and the customer relationship.