Page Speed Service fetches content from your servers, rewrites your pages by applying Web performance best practices and serves them to end users via Google's servers. To what extent your website's performance can be improved depends on a variety of factors such as the content on your pages, browser, geographic location of access, bandwidth, etc.
Google predicts that most pages will see increases of between 25 and 60 percent. Page Speed Service is currently being offered for free to a limited set of website owners. Visit the site to learn more and to gain early access to the service by filling out an application.
Eventually, says Google, the service will be open to the public and competitively priced, and those details will be forthcoming.