On Wednesday the 14th of October Google are no longer recommending the AJAX crawling proposal we made back in 2009 (http://googlewebmastercentral.blogspot.co.uk/2009/10/proposal-for-making-ajax-crawlable.html)
They openly advise now to use #! in URLs over ?_escaped_fragment_= .
Questions and answers
Q: My site currently follows your recommendation and supports _escaped_fragment_. Would my site stop getting indexed now that you’ve deprecated your recommendation?
A: No, the site would still be indexed. In general, however, we recommend you implement industry best practices when you’re making the next update for your site. Instead of the _escaped_fragment_ URLs, we’ll generally crawl, render, and index the #! URLs.
Q: Is moving away from the AJAX crawling proposal to industry best practices considered a site move? Do I need to implement redirects?
A: If your current setup is working fine, you should not have to immediately change anything. If you’re building a new site or restructuring an already existing site, simply avoid introducing _escaped_fragment_ urls. .
A: In general, websites shouldn’t pre-render pages only for Google — we expect that you might pre-render pages for performance benefits for users and that you would follow progressive enhancement guidelines. If you pre-render pages, make sure that the content served to Googlebot matches the user’s experience, both how it looks and how it interacts. Serving Googlebot different content than a normal user would see is considered cloaking, and would be against our Webmaster Guidelines.