Google's search results pages have been in flux the past few months, but it seems to have intensified the past week and then returned to normal.
Many search engine optimization professionals noticed significant shifting in their rankings over the weekend with some suggesting that these most recent changes are a reversal of an update that was put in place last week.
Most SEOs are simply at a loss as to what is going on but it likely portends a major algorithm update in the near future. While the fluctuations seem to be concentrated primarily on high-traffic keywords (which has reportedly benefited Amazon the most according to some reports), the best practice in situations like these is to hold tight and continue doing what is most important anyway - building links and developing content.
While no announcement has been made by Google, several search result tracking tools are showing significant spikes.