Many people have reported major changes in the search results since the last dance.

It makes me wonder if part of their refinement is to change the weighting of factors each month just slightly to make it exceptionally hard to game the search engine. It would be a logical move on their part. Most of the core powerful websites will stay in or near the top of the results while the sites that are most prone to the severe swings are those gaming the search engine heavily.

There will be some innocent sites that disappear, and some slop that rises to the top, but gaming the search engine has become a more fun and exciting game :)