Google is currently experimenting with "infinite scrolling" on Google search results pages. A Webmaster World user spotted a new box that replaces the standard pagination links: "show more results". When you click the message, Google loads the second page of results below the top results.
Google has already added infinite scrolling to its image search results last year in on July 20, 2010.
Google has tested a similar interface back in July.
There are many extensions that add infinite scrolling to Google search results pages. One of the best is AutoPager, which is available for Firefox and Chrome.
So instead of the bottom having click page 2, 3, 4 and so on, you get this button that reads "show more results" and when you click it, it will load the second set of results under the top result.
Google has confirmed it saying, "Google is constantly experimenting with new features."
Below is a screenshot of the feature and the video by TiChou demonstrating the feature: