I was offended by an ad I saw on Windows Live Messenger when I logged in to my computer at work this morning. I tried to uninstall it and use the plain-old Windows Messenger that comes with Windows, but that wouldn’t connect to my Yahoo! contacts (which all of my coworkers are on).
But then I found this blog entry on Ugly Chickens about how to block those ads with your Hosts file!
[UPDATE: Looks like this technique works for YIM as well!]