graeme_p - 1:44 pm on Feb 21, 2012 (gmt 0)
@steve, my site is not ad heavy and I lost the same day as well - on most page only one above the fold ad (admittedly a 336x280) and Vibrant and another ad below the content.
I think something else happened at the same time. What I am seeing is gains by large, multi-topic sites over smaller niche sites. Perhaps you do not have many of those sorts of competitors in the UK and Canada?