I feel kinda relieved. My best performing site also tanked.
I had ads above the fold. my content was thin. And I had a lot of outbound links!
But on another note, some of my other sites had seen no change. Difference, they are only ranked on a few keywords. Those keywords also don't receive a lot of searches. My best performing site however has a total of 80 pages and ranks for various terms. Lately it has been increasing in ranking until thursday the 17 and by 18 it tanked! None of the other sites are affected, thou they are lower perfoming sites.