Technology updates and quality improvements: This new release includes the latest versions of the Zend 1 Framework and Redis integration, as well as over 105 quality improvements throughout the product.
Automated functional testing framework: Community Edition merchants with in-house development teams can now access nearly 170 automated functional tests. This can help improve implementation quality and time to market by making it easier to do basic acceptance testing when adding extensions, making customizations, or upgrading.
Continuous security enhancements: Community Edition 1.9.2 incorporates recent security patches (SUPEE-5344, SUPEE-5994, and SUPEE-6285) into the core code to help merchants better protect their sites. Merchants on earlier versions of Community Edition should apply the patches to fix these critical security gaps, or upgrade to Community Edition 1.9.2. View the latest security information on the Magento SECURITY Center.
The full list can be read in the release notes: http://merch.docs.magento.com/ce/user_guide/Magento_Community_Edition_User_Guide.html#magento/release-notes-ce-1.9.2.html