Several guides for various parties interested in Facebook are available below. If you know of any more we should add, or would like to give feedback, by all means do so!
The Guide to Facebook for Librarians
Laurie Bridges has a presentation that relates some of the possibilities for librarians from the standpoint of education. She later expanded this topic to include the possibilities found in applications.
Conducting Digital Ethnography
Use of Client-side Scripting for Facebook Research
If Eric ever has time...
Facebook as a Tool For Learning Engagement
Fred Stutzman wrote a reasonably good guide for educators in his blog about a year and a half ago and much of the wisdom present there still holds true. Though Facebook has changed in many ways since then (applications, the Newsfeed, Facebook pages, built-in chat, and very different privacy settings) it's worth consulting. We may look into an update sometime in the future, but for now, go see what Fred has to say. He followed it up with a sort of top-ten rules post just a month later that addressed skeptics a little more directly.
Oh and then there's a Facebook group about the topic, which could also make for a good resource.