I've noticed that for my niche, the amount per click has gone down the last couple of weeks. Yesterday it went down a lot. I keep ongoing records on a spreadsheet so I can tell that this has been happening over the past 2 to 4 weeks. Yesterday, though, was the worst day I've had in months as far as earnings per click is concerned.

Also, does anyone notice that as the day goes on, the earnings per click goes down too? In the morning, I usually start pretty high and by evening there's a steady drop down.