Yesterday, I had to add Yahoo IM client to communicate with team members of a project I've just joined. With three IM clients running (MSN, AIM, and Yahoo), I had three contact lists and UIs to get confused with. Yikes. Then I remembered Trillian which supported all three IM protocols. It took me about 5 minutes to replace the three IM clients with Trillian. So far, I've had no problem at all and am happy with it.