There was a flood of reports over the weekend by Google AdSense publishers complaining their AdSense earnings was as much as 50% lower than the estimated earnings they were projected to earn for the month of October.

We have threads at WebmasterWorld and Google AdSense Help with complaints of the major earnings difference. Here are some select complaints:

I personally checked my earnings and they are pretty much the same as my estimated earnings. But there are tons of reports of huge differences between the estimate and actual numbers in the forums.

I have yet to see an official Google response yet.

Forum discussion at WebmasterWorld and Google AdSense Help.

Update: Google posted this is now a known issue, saying:

The issue is said to be resolved, here are the details: