At my "day job" we use instant messaging regularly. We are an international company with over 28,000 employees in offices scattered over six continents. IM helps smooth out collaboration by allowing fluid communication. In an instant, I can check to see if my colleague is online and at their computer, eliminating phone tag and email lag.
Our corporate IM system is IBM Lotus Sametime, which allows us to quickly share our desktop for collaboration, support and training.
I regularly get direction from my boss via IM and use it to collaborate with colleagues. IM plays an integral role in our knowledge management system, facilitating people-to-people connections and informal knowledge sharing.