Some quotes from Google Blog
The Google doodle tradition started a long time ago (in summer 1999, in fact) when Larry and Sergey put a stick figure on the homepage to signify that they were out of the office at Burning Man. Nothing against stick figures, but our logo designs have become rather more varied since then. Today you’ll see a special design that commemorates our 10th birthday. We’ve incorporated a little bit of history by using the original Google logo from 1998. And since everyone keeps asking what we’d like for our birthday (besides cake and party hats) — the first thing we thought of was a nice new server rack. Posted by Marissa Mayer, VP Search Products & User Experience, and Dennis Hwang, Webmaster .