This is a beta application. Moreover, it is even integrated with AdWords and free to all advertisers. Google informs that in a matter of few weeks this feature would be available automatically to all the Adwords Advertisers in their account.
The press release states:
Google Website Optimizer is designed to help website owners increase conversions such as sales, sign-ups or downloads. This multivariate landing page optimization tool enables marketers to test different ideas for web page content such as different headlines, promotional copy, or images. The application provides easy-to-read reports that enable advertisers to see which variation resonated best with their site visitor. It is a self-service application that enables website owners to set-up and run multivariate landing page experiments.