On Sunday, all of my sites (they are connected to one Google authorship acct) were nuked, dropping from 1-5 in SE rankings to 10-15.
I don't know what happened. Some kind of manual review.
How many sites went down? half? all of them? are they all hosted on the same server-ip? do all of them have organic traffic? or some feed from the traffic of a big one?
Being linked to the G+ account sounds like something to look upon.
Otherwise consider server problems, it happened before. Be it due to intermittent downtime or dirty ips due to bad neighbors. There must be some clue, did you post something around the week the problem appeared?