Recent reports via WebmasterWorld note that several Webmasters made changes to their pages, specifically the title tag and the H1s and their rankings dropped drastically. Now, I assume these text changes were not incredibly drastic, where they changed the term they are targeting from (example) "Search Engine Optimization" to "Big Blue Pineapple Chair" (ah, it has been a while since I mentioned that chair).
Some specifically note that the changes they made were minor in detail.
It makes you wonder, if making any change to your page can have a drastic affect in your organic rankings at MSN Search. One Webmaster reported that his rankings are returning to normal.
There does not seem to be an algorithm or index update taking place at MSN. So it seems to be totally dependent on Web site changes.
Forum discussion at WebmasterWorld.