There are dozens of reports via WebmasterWorld that Google has sent out emails to their publishers telling them they must update their tax information.
The subject of the email was "Action Required: Please update your tax information" and it was sent yesterday, on Thanksgiving.
The email stated that these publisher's tax-identification number (TIN) and the taxpayer name do not coincide/match. The emails did not appear to be phising scams, because the URLs did send the user to the proper source.
It may just be that a multitude of AdSense publishers were missing details from their tax information page. I did not personally receive the email and my account looks to be in good status.
Forum discussion at WebmasterWorld.