marketingmagic - 11:58 am on May 19, 2011 (gmt 0)
This is exactly what I've started to see as of 10AM on Tuesday. Some drops on core terms, but primarily restricted to long tail terms where product pages with thin content were appearing. These long tail terms, in some cases, have been bumped 5-10 spots, in other cases are gone completely, and in other cases, haven't changed at all - yet traffic for the terms that "haven't changed" has dropped - which in my mind does validate Robert's theory.
Overall I'm seeing about a 10-15% drop in Google traffic since Tuesday.