aristotle - 2:36 pm on Jun 10, 2012 (gmt 0)
Was it possibly the 26th of April?
My site seemed to be ok on the 24th and 25th, but tumbled on the 26th.
Planet - I remember we were talking about your site in another thread, and concluded that it was probably inflicted with a penalty on one of its keywords. The site could have been hurt by a link devaluation as well of course, but a big drop like you experienced for that keyword was probably mainly due to a penalty.