Don't consider this definitive, since I haven't spoken to any of the other people behind the scenes, but it's not really an idea that thrills me, personally.
For one thing, Facebook shows a lot of signs of driving users away, no matter what they claim about the benefits of advertising. I know you're not talking about advertising, per se, but it's still something of an issue.
For another, my feeling is that the relative smallness (and steady growth just by word of mouth) of the community here is its strength. It's very much a "small town" atmosphere, rather than Wikipedia, 4chan, or any of the other large online communities. This is one of the very few areas where we don't have people bickering over what artist is better or how modern books are SOOO much better (or worse) than older books.
Along similar lines, I would also worry about the level of support required. I don't really like the idea of waking up to another twenty people who can't be bothered to read to find out how to open the files, feel the need to complain about scans from microfiche, or that we dare to contradict what "everybody knows" about copyrights.
Again, don't consider that official, because we haven't discussed it. And there might be perfectly valid reasons to tell me I'm full of crap. But for the most part, I don't see a real benefit to loitering on Facebook.
