I've been experimenting with Facebook pages (as well as lots more!) over the years. In one institution that I'm associated with these have only been accessible on phones or via proxy browsers in class so of little use there but, after almost zero activity of value for two years, I have found a remarkable increase in the last few months by students and colleagues from home and discussions, sharing of thoughts, constructive comments and links to pretty relevant resources surprisingly (to me!) unlittered with rubbish or 'I'm just getting Luke to make me a sandwich' stuff which they now seem to reserve for their own personal pages.
I won't pretend that anything marvellous is happening but it's a familiar, dead easy to use environment and the new input each week has been something I have been able to refer to and expand on, or encourage more research into, in normal sessions. In particular, I've seen students helping each other with tasks and saying what they think about topics which doesn't seem to be happening much on the VLE.
In another institution access is not initially restricted and although one or two tutors have set up course or module pages none seem to have had much impact. It really does still seem to be something mostly used out of the classroom. This place has installed a control mechanism that enables tutors to monitor students' screens from a staff pc and as purely social use gets their access pretty smartly cut there have been quite a few mistakes as it was difficult to distinguish a personal page from an 'approved' one! I guess the topic (project management) hasn't lent itself to as much interest in research and sharing there as the other (web design) where there are links and visual interest a-plenty.
What does appear to be working well are pages set up in some Work Based Learning sectors I've been involved with. All the participants are adults and spread out across the planet, occasionally meeting for practical workshops. The simplicity of creating photo albums, for example, has enabled people who I know have pretty low ICT 'Office-type' skills to share examples of what they've done at these workshops. Discussions do have regular and generally organised input and a little direction from tutors which helps a lot. The main purpose of the pages was initially just to promote an organisation's events and activities and the inclusion now of nice comments, images and links to resources has had the pleasant effect of enhancing its image and their workshops.
There's nothing being done here that couldn't be done using other applications but Facebook just kinda works for many. I certainly wouldn't describe any of this as particularly significant, however, as there are lots of new tools around and coming up which enable more efficient and manageable delivery of course materials and interaction which will, I feel, be ultimately be preferred to facebook (unless fb develops its own app further in that direction!). In particular the advent of sites people can contribute to (and tutors edit) simply and the marvellous RSS feeds from tutors, students and authoritative source blogs will make a big difference to life in the classroom. Twitter is also proving to be an excellent tool for finding and sharing really up-to-the-minute ideas and resources and, indeed, many of the most valuable posts of those facebook pages were, in fact, auto feeds from Twitterfeed or similar!
Lastly, here's a video I found of a recent discussion in the States that you may get colleagues talking too. Some odd spelling in the comments - not mine, I should add!