cj2600 - 1:03 am on Apr 24, 2013 (gmt 0)
Exactly same problem here for my and my wife's account. Same 60% drop starting at the end of March. Earnings are ridiculous, back to 2007-2008 levels.
There is nothing you did wrong. It's google related changes and THERE IS NOTHING you can do about that. Just relax and live each day like it's your last day with google.
I've seen drops like that a few times since I started my sites in 2005 but never as bad as the last one. First times were very stressful. Now I'm just taking it as is.
The good thing I got my life back. I stopped working all those countless hours supporting my sites and answering countless comments on my blogs. I just let it go as is posting occasional posts. I stopped checking my google account every 15 minutes a while ago. :)