Google Themed Ads for Christmas

Whenever themed ad units are available, google adsense display them only to users in the appropriate locations, as determined by user IP address. For example, Fourth of July-themed ads would be visible only to users located in the U.S., while users throughout the world might see ads with a New Year's Eve theme.

You can enable or disable themed ad units by following these steps:
>Log in to your account at www.google.com/adsense.
>Go to the My Account tab.
>On the Account Settings page, scroll down to the 'Ad Type Preferences' section and click 'Edit.'
>Depending on your preference, check or uncheck the box next to 'Enable themed ad units when available.'
>Click 'Save changes.' Your selection will apply to all your AdSense ad units.

http://googleblog.blogspot.com/2005/12/decking-halls.html blogs that Unlike the fruitcake, though, these ads don't last for years and years – they're just present until December 26.