Today, Google announced the launch of Caffeine, a new web indexing system. To quote from the information received,

"With Caffeine, we analyze the web in small portions and update our search index on a continuous basis, globally. As we find new pages, or new information on existing pages, we can add these straight to the index. That means you can find fresher information than ever before — no matter when or where it was published."

To see how Caffeine looks, here is the Google diagram.