Meebo

it's great when i use it on someone else's computer...

There are two primary reasons to use Meebo: 1) If you are on a shared computer or your work or school blocks IM access 2) If you want to combine all of your IM identities in the same place. You can log in once to Meebo, and have access to your Yahoo and MSN buddies. Performance is not quite as good as the downloadable clients, but a Web based service is so much less intrusive.