In 2009 Google released a proposal for making AJAX based
The original proposal can be viewed here:
The proposal set a scheme that allowed search engines to accept static pages with matching content to pages that are loaded with AJAX without violating Google's guidelines.
In this update, Google have announced they are now capable of indexing AJAX based content without aid, deprecating their earlier proposal and encouraging webmasters to allow Googlebot access to the page's CSS and JS.
There are several big news and call-to-actions in this announcement for SEOs and web builders:
Google strongly encourages site builders to follow the new guidelines, so it's safe to assume they’ll eventually stop supporting the AJAX crawling scheme.
Google’s official announcement can be viewed here: