Ever been on someone else's machine and needed Messenger? I have. Now you can do it all through the web... very cool. I wonder if this breaks down the firewall issue if you're at a location that blocks it.
[Update 1/26/2006]: Comments disabled for this post... to all of you who keep posting comments to this post: I can't do anything about the fact if your provider has blocked not only IM clients, but also the URL for the MSN Web Messenger.