The majority of keywords are being used by other organisations in the same industry and I know they are not bidding anything like $6.50 . . . most are bidding around $0.25 - $0.35 ea.
For the past 3 weeks I've noticed it varying dramatically over a weekly cycle - EPC at weekends is obly about 80% of what I see mid week.
This is in addition to the weekly cycle on visitors and the weekly cycle on CTR.
Week ends are getting to be a waste of time - amybe I'll turn my ads off (or reduce my bids) at week ends. Maybe lots of other already doing this is the cause of the problem.