that you put a fresh adsense code on your page your earning are 3 x higher in the first 2-3 days than the rest of the time they are in service. I found that if I request a new ad code every 3 days my earnings double or triple on that single ad.
I have noticed this on brand new sites with an uncommon niche and Google was having trouble targeting the ads
It doesn't neccessarily mean that. I, somedays get .25/click and then the other day i get .87/click, without changing the ad code. It all depends which ad they click [top ads pay more]