Back on March 16th it seems Google started an algorithmic search ranking update that continued on for a week or so. In my opinion, the number of webmasters who took notice of this update was minimal compared to a Panda, Penguin or Fred update but those that did get hit, saw huge declines in Google traffic.
Google has yet to officially confirm this update, so it makes it hard to give you anything on the record. I am trying, but so far, still unsuccessful on the confirmation.
Can you all check your analytics for your clients and your own sites and let me know if you were hit at all. I guess take the poll multiple times per client?
Here is the poll asking How Were You Impacted By Google's March 16th Update?
Forum discussion continued at WebmasterWorld.
This post was scheduled to go live today but was written earlier - I am currently offline today.