I have never managed to break through the $100 a day barrier with Google Adsense. I have been very close on a number of occasions but never managed to limp over the three figure line.
The usual pattern over a couple of months is that adsense earnings build up and continue northwards and then suddenly fall back (usually at the beginning of a month). It’s like I am always starting over again and I find it impossible to have an consisitency.
On the other hand my affiliate links are much more stable in terms of income and much higher. I am considering ditching Adsense soon on sites where I have a steady affiliate income. There is nothing more annoying than getting 10 clicks and earning 50c for all of them! Some call it smart-pricing, I call it getting cheap traffic.
So I would strongly advise people to look at the affiliate side more. It takes more setting up and work to manage things but the financial rewards usually outweigh the extra maintenance.