Even if you are an “AdSense Veteran” this is worth looking into. I do find Google’s statement under the “How much you can earn” section quite humorous:

For example, for every thousand page impressions you receive, you might earn anywhere from $0.05 to $5.00. While most publishers will fall within this range, you might notice that it’s a very large range.

Seriously, if you are earning 5 cents for every 1,000 page views, it is time to get out of the web business.

Google AdSense Newbie Central