I made an excel spreadsheet of the Google reports using the date range of "All time". It's very interesting just looking at a regular chart with the data they mention. What I saw was a very minor improvement in terms of impressions. Since being given ability to choose color and to switch to leaderboard, the CTR jumped to more than double. As did earnings. Tweaking your site in terms of where and how to display the code really can help tremendously.
I added an extra column called Earnings per click. It has been slowly, steadily going down from the beginning. I suspect this is the thing for us to watch to determine how well the profit-sharing cut goes in the future... It is possible that more pages were shown with less profitable terms, but I'm not really sure. Would be nice to know if others also seeing a downward trend.
Clark...want to have a little more fun...hit that chart wizard and plot out the trends. Then will see the trends. Have this for CPM, EPC and $/visitor, click percentage etc. Interesting results and trends over the last 2 months. When you trend in this fashion can see increases and decreases and more importantly the effects throughout the month.