there are many pros and cons here; one of the pros being that file-sharing can occur on facebook (within copyright law) but we don't allow attachments on here (largely for the anti-virus angle as well as copyright control)
 
a facebook group would be hard to moderate (i doubt anyone on the jsm editorial board would have the time or inclinaion to do so), and as such the new group could not have anything like "jsm" in the title, as the Journal could not be affiliated with an unmoderated group that was not under its control (in much the same way that any brand name will expect to be treated in that fashion)
 
anyone here is quite free to set up external groups that discuss similar subject areas, and to invite readers here to join. Posting that ONCE, i would sugest. But this list is for a specific purpose, and it could become quite bothersome if the majority of a person's postings on any topic were "hey, there's a really interesting thread about this on my magic-academic-facebook site right now!!".... there are also problems of permission; this is a non-public forum, and if someone's comments were taken out of there and posted elsewhere without their specific permission (or indeed to somewhere where they were not a member) there is a whole host of issues....
 
ditto MySpace, ditto Blogger, ditto Livejournal etc
 
There is also the problem that (in the UK at least) many of us look at JSM e-list threads on email while at work, and a lot of British workplace computer managers have blocked access to social networking sites like facebook as they are, as a poster here remarked, a major time-suck
 
dave e