Over two years ago, Google started testing AdSense optimization reports, also known as automated AdSense tips. They can be found when you go to your AdSense Inbox.
A WebmasterWorld thread asks, why does Google not send AdSense optimization report every month? Personally, I have not received one since December 2008 and I am happy that I have not received one. Here is a screen capture of my reports in my AdSense inbox:
I assume the tips don't show every month because (1) they are often repetitive and (2) can be dead wrong on occasion.
One WebmasterWorld member offers another possible reason, "They laid off the tip writer." Of course, he is joking.
Forum discussion at WebmasterWorld.