Today (or tomorrow, depending on where you are) there is a special Google logo on many Google properties and likely will be in Google US very soon. You can see the John Lennon 70th birthday Doodle / logo on Google UK and other Google properties as well.
John Lennon would be celebrating his 70th birthday today. He was born on October 9, 1940 and died on December 8, 1980 (I was born that year).
What is so special about the logo outside of it being for John Lennon? I believe this is the first time Google used a YouTube video as the Doodle for the logo. When you click on the logo, it flips you into a YouTube video and then when the video is done playing, it takes you to a search result for [John Lennon].
A screen cast of the action:
The YouTube video by Google as played on the Google home page:
I should note that Google Argentina has a doodle for Cesar Milstein, not John Lennon. He was an Argentine biochemist in the field of antibody research and was born today, October 8th.