Under the assumption that everyone else in the office is using such a thing as Facebook at Work, all employees should use just to keep up with the joneses as the saying goes. If it becomes a useful work tool for companies, it would be like using any other advances to do your job and keep informed as to what is happening in the workplace.
I don't think it's a very wide market of people that the Facebook at Work would be targeting. I would think most people work a full day without ever seeing a computer, and would have no use for it. Those who do have a use for a "filtered" version of Facebook already have similar products available, and it would be difficult to convince them to switch their already existing social networks as well as difficult to get employers to "unblock" Facebook from their servers and convince them it's for productive work-related things. People are so used to the Facebook name being attached to, basically, ways to waste your time - playing games, socializing with friends, etc. I don't think they'll get out of that stigma and be able to penetrate a serious work-related market.
I would not use 'Facebook at Work' if it came to my office, as I already think Facebook knows too much about me, what I do, and who I socialise with. I would not really want my work and my social life to mix, as I would find it hard to switch off after finishing work.
Office work and Facebook are two entities that should stay far away from one another. People are getting into trouble with their bosses for being on Facebook in the first place. I think work would never get done and this is another ploy for Facebook to breach workers information and sell it on the Internet for profit. Nothing good can come out of this situation.