What a wild weekend. Most of my sites enjoy some very good rankings in MSN search, and I recieve good traffic from it. However, it looks like they were doing some algo tweaks over the weekend. I was nowhere to be found in the SERPs, while previously unlisted sites were appearing at the top. I suspected it would go back to normal today, and it looks like it has. Good thing all my eggs are not in that basket, that would just be stupid.
Here is a discussion on Webmaster World about it.