I don't find that to be the case either. Anecdotal, obviously, but I've worked for companies that range in size and I never add anyone from work on Facebook. Same goes for my wife.

We joined Facebook in the early days when you needed a .edu email address to join, so I've got a lot of college partying photos up there. I've always seen it more of a private space. Not sure if the time you join and your original perception of the service changes your use.