"By default the script will override your favorite doodle on holidays or any days with a special doodle (personally, I never want to miss a new doodle on the Google homepage). After the holiday is over, your favorite doodle will be back. However, you can change this preference so that your favorite is always shown," mentions the author.
Unfortunately, the script is quite complex and it only works in Firefox, assuming you've installed the Greasemonkey extension.
For iGoogle users, there's a gadget that lets you pick "one of the past Google holiday logos to sit atop your page, or have it cycle through them randomly".
{ via Search Engine Land }