I was writing this as a comment on Bill's post, but it got long enough to be its own...
It's been interesting to watch all these social media or 'web 2.0' platforms -- blogs, networking sites -- move from being purely social to being important for businesses. Our parent company certainly has several pages on MySpace, Facebook, etc.
I think where you might be more ahead of the curve, Bill, is in your thinking of a FD as a business that needs marketing. One of our columnists, Jason Zigmont, wrote about this too: Marketing Your Department, though he was talking about marketing for recruiting.
Any business doing marketing these days is looking at these new platforms. Partly because, as you say, they're FREE, they're much easier than even getting a print ad made, and they reach very specific audiences of interested readers. I think if you're marketing your dept. for recruits, outreach or whatever, I think twitter et al are right on target.
(Incidentally-- I got to thinking about the original social networks when I posted this article.)