I actually only recently got a Facebook account, and it was 100% due to work. My company is using Facebook to share things like pictures, videos, etc. (non-proprietary) with the employees.
Just one anecdotal comment of course, but just trying to point out that Facebook is becoming more than just social networking.
Full disclosure: I've been on LinkedIn for a while, it's only Facebook that is new to me. I have never been on myspace.