[robwilliams]

Microsoft uses Yammer as its corporate social network (obviously), and it's pretty active. Since teams working on the same product are in different buildings/cities, there's a group for each product/feature/team and people ask and answer questions pretty frequently. I personally use it as a public knowledge bank to search for solutions to issues I'm having before sending out a group email.

For smaller companies where all employees are in the same place I guess it wouldn't have as much value though.