A WebmasterWorld thread named Bet on Google Paying Early in December says it all. Yes, as expected, Google has already started the "PIP" or payment in progress notifications to their AdSense publishers this month. Why was it so expected? Well, if Google's fiscal year goes by the calendar year and ends on December 31st, which I believe it does, then Google wants to spend spend spend, as much as they can before the 31st to get all the deductions they can possibly get before the new year starts.
You can check yours on your payment reports screen.
An early Christmas gift or Google's tax accountants working those IRS rules?