You’ll only see it today, May 10. But this might work later.
I don’t remember them doing this last year. Does anyone?
Okay, there must be somthing wrong with my computer because I didn’t see any special logo when I clicked on the Google link in your post. Nor did I see anything special when I manually typed in http://www.google.com in the address bar. 
But thanks for providing the link to the GIF, rowrrbazzle… that I could plainly see. It was interesting. 
And no, I don’t remember them doing anything of the sort last year: only for holidays such as St. Patrick’s and Christmas. (or maybe they introduced the holiday logos this year too… I’m not sure)
Google has a whole page of their past holiday logos :
Other artists they’ve honored so far are Claude Monet (Nov. 14) and Piet Mondrian (Mar. 7).
Flamsterette_X, it was there when I tried it but now it isn’t. A bit of searching revealed that Dali’s birthday is actually the 11th. The logo was probably up there briefly in error or for testing.
Odieman, I saw the Mondrian, too.
panamajack, thanks for that link. I’ve seen most of them, and it’s nice to catch up on the others. I don’t remember the Monet. Any chance you have a link for it? I tried logos/monet.gif and got a “page not found”.
Hey, I lost my cookie so my post disappeared.
I had a direct link to the Monet logo, but you can find it further down the holiday (I guess that should be ‘special occasion’) page. It’s organized backwards in time as to when it showed up on their page, so something that was up in April 2000 is further down than something from October 2001. I rather liked the Monet, it’s even signed by him.