I have also been seeing a lot of flux over the last 3 weekends. We are a new site, and have been slowly working our way up the SERPs. Usually, during the week, we rank on the first page for more long-tail keywords, and on page 3-4 for our top most competitive keywords. However, when I check the Webmaster tools, I see that the have our top search queries as the two most competitive terms, and list us as showing up at #6 for both. The only thing I can think is that we are appearing in the first page over the weekend and then drop back down over the week. That just seems really odd to me, so I'm not entirely sure what to do at the moment. Any thoughts or suggestions would be much appreciated. Thanks.