Search Engine Guide reports it’s seeing signs of an oncoming "Google dance," the introduction of an algorithmic change that could have major effects on who gets listed among the top sites for each keyword.
Google is conducting a house cleaning stemming from what appears to be an algorithm update. Several SEOs have noted the typical precursors of change including a decrease in counted back-links and minor fluctuations in page-rank values. For the past few days, Google’s results have been bouncing, with placements moving up and down frequently.
The site indicates that among the big losers appear to be those who have had their sites linked far and wide from irrelevant web content. If true, this would constitute a setback to comment spammers and other annoying web "marketers" whose effluent of links -often found in discussion areas of sites – pollute otherwise relevant content.
I have noticed a big fluctuation in search rankings at many of my clients web sites. No doubt having a lot of fresh quality content and links from other sites that are similar to your sites theme is the way to go at Google at least. MSN and Yahoo are also very important and can not be forgotten. Sometimes people just focus on Google and forget about the other search engines which can also produce focused and qualified visitors to your site.