What is IM used for in the workplace?

My office mates and I figured out this week that we have an IM client on our corporate workstations. Novices to the world of corporate IM, we don't really know what it's used for. I've used IM clients at home, of course, but never at work and we're all at a bit of a loss on how this would be useful, if at all.

A quick session of searching 43f reveals that most of the discussion up until this point has been about managing the distractions of IM and managing your coworkers' expectations of your responses. But I'm wondering, what's IM used for in business? So far in my office, people have started chat sessions with entire work teams present online and left the session open all day. Team members will post questions or comments or requests to review edits on shared documents. In one of our groups, the director has moved some of his communication to the chat room, with the expectation that his team members will read this message during the next hour or two. Is this a typical use? How about one-on-one chats with colleagues?

Tell me what IM looks like at your workplace.