The latest update of the Google algorithm, named Panda 2.0 was released a few days ago. It was an expected update and apparently affected the rankings of a small percentage of sites, mostly in the US.
To check the status of your website, track the organic traffic from Google in your analytics program. If you see a sudden drop between 13-15 May, you are probably affected by Panda 2.0. So, in order to solve this problem, here is what you should know and what you can do: