CainIV - 5:46 am on Mar 30, 2012 (gmt 0)
I think the degree of action, and the time-to-action vary depending on the severity of the infraction.
I have seen some websites who I am in communication with regularly drop over 50 spots weeks after receiving these email.
And others that haven't budged, over a month later.
Ultimately it could be as easy as Google sending this message to those that are legitimately using tactics that they shouldn't be.
And let's face it, the campaign could be about gaining information. After all, what better way to get a quick amount of data back about links and link arrangements than have webmaster snitch on sites that sell and indict others that advertise there?