Google Artificially Promotes Recent Web Pages:
Google paid a big price when it started to index pages faster and show them in the search results minutes after they're published. The problem is that you can't rank a page that has just been created because it has no backlinks so Google artificially inflates the rankings of the recently-created pages based on historical data and the few backlinks that are detected.
In some cases, if Google sees a lot of searches for a query that wasn't popular before, it assumes something has happened recently and shows more recent results.
These two changes are extremely visible today. If you go to Google's homepage and click on the special logo that celebrates 25 years of TCP/IP and the New Year, you'll be sent to the search results for [January 1 TCP/IP] and you should normally see a Wikipedia page as the top result. But the first page of Google's results has changed dramatically in the past hours and all the results are new: most of them are from spam sites, pages that discuss Google's logo and quote from Wikipedia. Most notably, the top result is a Digg page that links to a newly-created blog with a meaningful address: january-1-tcp-ip.blogspot.com and a highly-optimized title: "January 1 tcp/ip". Obviously, that blog hoped to take advantage of Google's new logo and succeeded: the two top results are Digg pages that link to that site and they're followed by that blog's homepage and a post from the same blog.
The site gets traffic both directly from Digg and from Google's homepage.
You can see at Google Trends that [january 1 tcp/ip] was the "hottest" query for December 31 in the US and continues to be very popular today.
It seems that Google can no longer send users to a search results page from a doodle because the results can become unpredictable and they show a big flaw in Google's algorithms. The same bug can also be a feature if there's a devastating earthquake somewhere on the planet and people start to search for more information about it after they hear the news.
Update (9 hours later): Other blogs take advantage of the situation.