A nice early Christmas present from Google for Adwords advertisers, if you were lucky enough to be on the receiving end of this. Only my seasonal campaign seemed to be affected, I would guess due to many people doing holiday related searches - my other campaigns were normal without any overspending.
Since 2/3 of those clickthroughs were for content sites, Google will be out of pocket $$ after paying AdSense advertisers for those clicks. (More on this from an AdSense publisher's point of view [webmasterworld.com])
I do admit that I nearly had a heart attack at first glance of my stats, hoping I had set the daily limit at what I thought i had ;)
<added>Looking back, I am guessing my other campaign did not go over my daily limit because I did not have top positions for many of those keywords. Many of the ads were well underserved, even for a Sunday. Without the daily spend checker checking, Adwords would have just kept serving the highest paying ads, without rotating to some of the ads in the lower positions when the first place ads were nearing their own spend limits</added>
me too sunday huge over spend on max daily spend.
Yeah, this is an expected behavior after an update such as the one that occurred on Sunday. Your ads were still showing as usual, but stats were not being updated - and the systems that prevent overdelivery will run behind.
So when stats catch up, there can easily be an overdelivery. As Jenstar pointed out, if we've exceeded your budget by the time we bill you, you'll automatically be given an overdelivery credit.
In the advertising world, this is what we fondly call Free Advertising ;)
AWA