Google have recently announced that they are withdrawing support for their Bot for AJAX crawling. There were talks of discontinuing the support for AJAX crawling and it has been confirmed now with the official announcement from Google.
It is said that Google no longer supports the AJAX crawling method of its bot, but that does not mean AJAX website will not be crawled. AJAX websites will not be crawled only of the GoogleBot is from crawling a websites Javascript or CSS files.
Google has said that they will not be supporting AJAX crawling anymore but will not stop their bot from crawling AJAX websites but have recommended that since they are withdrawing support to AJAX crawling they encourage to build future sites based on progressive enhancement.
If you have already implement AJAX on your website Google recommends to change your methods going forward. If the current site that one has built has AJAX crawling Google recommends that it is important that best practices are followed for websites that will be newly built and also for the websites which are undergoing changes. Google recommends to avoid escape fragment URLs.
Regarding Webservers that pre renders pages, Google recommend that the content used in the website matches the needs of the users on how it looks and feels. Presenting a different content to the Googlebot than what the user needs will be considered cloaking which will be against the webmaster guidelines.
