goodroi - 6:29 pm on May 25, 2010 (gmt 0)
For those that are seeing a traffic decrease but arent sure where there drop is happening on the website here is something that you might find useful. This is more for people that havent been tracking Google rankings.
#1 - Grab the top keywords for May 2009 and May 2010 (make sure the dates match up and you take a long enough sample). You can use Google Analytics or your log files.
#2 - Compare the keywords traffic year-over-year. You'll probably see some keywords went up and many more went down.
#3 - Identify the biggest changes and then visit the serps for those keywords. Maybe your ranking is down or your indented listing is gone.
For the websites that I have done this with I have noticed some very interesting trends in which keywords are impacted negatively. The more information and research you have the better you'll be able to respond to this latest change. enjoy :)