From the release notes:
Fix for CTRL-Z for shutdowns. Many updates for JSON server. Improvements completed on Catalog support. ZeroMQ and Gearman supported updated. Updates AUTH_HTTP authentication module. Documentation enhancements. Testing framework updated. Regex Policy updates.
Stewart can say a lot more about Catalog support, but this is one of the cooler bits of work that is happening ongoing. The original work was began for Rackspace and continues today. Virtualization inside of the database is long overdue.
The JSON server is another one of the locations where we see a lot of effort. Being able to support JSON queries directly seems to resonate with a lot of folks today.
For the record I wrote zero lines of codes in this release. Work continues, and in the case of Drizzle it is all about work coming in from the community :)