Not sure why one would need a work specific social network. Work != social, at least for me. I've never shared anything or wanted to on my fb with my work colleagues.
We were just talking about doing a work only social network, with basic bio info, a photo, and background. We have been growing rapidly and it's getting extremely hard to keep everyone's info straight. I know that it's going to be useful for me since I end up working across departments fairly often. Do I expect everyone to get value from it? No. Will it make the workplace magically better? No. But it will give us the tools to be a little closer as a company, and hopefully promote cross team communication.