Google MayDay Update
6/9/2010 10:00 AM
Search engines like Google are constantly changing their algorithms they use to process, index, and rank your pages. In fact, Google has done that over 500 times last year.
On May this year, Google confirmed to have made such a change and it appears to be fairly substantial. The change has caused many sites to loose their positioning and while it seems to be specific to certain types of keywords called long-tailed keywords (keywords with 3 or more words) Google never releases specifics and at the moment there is no clear way of determining how your site would have been affected.
One way of determining whether you were affected is checking the crawl/indexing rate using the Google Webmaster Tools.