On my site, I have gone through spurts where I am getting .05 per click. about two weeks ago I switched it to image ads for about 1 week to see if that would help on ctr but the pay for the clicks were surprisingly low considering a image ad takes up an entire block of ads. At the end of the day it I usually end up with an average of .21 to .23 per click which isn't all that bad I guess . It's just funny when I log in and have 10 clicks for a total of .47 and then an hour later I have 15 clicks for 4.08 or something. What is your average ppc? In addition, what is your average ctr? My ctr averages a tiny 1.4% for this month.
What area are you putting your ads, and what is the focus of your keywords. I find that I get weekly and monthly variances dependant on the day and time of year. Also I haev come across people who can run hour bit monitoring and will add sharp variance over a single day