muchacho - 2:26 pm on Jul 1, 2013 (gmt 0)
"Last three days of June just dropped like a rock. No reason I can see for it. Hope July is better!"
Depends how big the rock is.
Some people have had issues since 26th June and some from yesterday/today where text ads CTR has nose-dived, yet image ads are ok, which suggests an error at Google's end.