Seems like the same situation as what I am getting too, my sites are UK bound and all run on WordPress, only one of the wordpress blogs have been affected.
Sadly its the old'est of the blogs almost 3 years old, run identical mods and SEO tactics.
My traffic graph looks like a roller coaster at the moment, up and down...
Though the fact that before May my traffic came back for a few days hints to me that Google is pretty much broken and is being fixed.
I hope that is the case!
I will keep you all posted if traffic comes back and rankings return.