Yahoo, Google and Ask Jeeves all are sporting customized logos for the holiday season. When you go to Yahoo.com and click on the top center logo it takes you to http://events.yahoo.com/holiday05/. When you go to Google.com and click on the middle center logo it takes you to Google's first of many holiday season doodles at http://www.google.com/doodle10.html (more to come). And if you go to Ask.com and click on the Jeeves logo, it takes you to a search results page (as a search engine should, imo) for http://www.ask.com/web?q=Happy+Holidays. Now Ask was sporting a snowman logo yesterday, so they are changing things up, possibly daily for the holiday season, keep and eye on them and Google for logo changes.
Folks are discussing the Google logo at DigitalPoint Forums. And I started a thread for Ask Jeeves at our forums here.