peterdaly - 2:23 am on Jun 14, 2010 (gmt 0)
Could be an algorithm tweak of the mayday update.
I had 350k of monthly visitors wiped out due to the Florida update years ago, but it was much different for me than most others. Traffic for most people affected dropped to nothing all at once. For me, the update was a non-event...but the turning point in my traffic growth as the screws on the duplicate comment filters were slowly tightened. It took about six months to go to zero...but it is clear that florida is when the root cause happened.
Mayday could be similar...especially since goggle publicly acknowledged the change.