At my job, work is about 50% IM.
Perhaps that is because an employee in New Jersey reports to a guy in Columbus who reports to a guy in the UK who reports to a guy in New York.
With the teams scattered so radically, we'd never get anything done without IM.
When I worked in IT at Bank of America, we had an IMing system set up and reading the logs for that system was basically just reading sex talk.....and jokes and gossip.
But most of the working divisions there were centralized within themselves.