SEO industry insiders have noticed a marked change in rankings over the last few weeks.  Some speculate it will impact Google Local listings with a map update.  Others have cited industry-specific moves.  Still others are thinking that these moves are in anticipation of a major update which is forecast to happen around May 23 if G sticks to its pattern.  Time will tell.  In the meantime, further evidence that there is something going on can be found in this article.