There are a ton of changes in this release, and you can get into the details in the change release notes. For the Mac version of the software, the biggest news is that PowerPC is no longer supported. If you’re still holding on to an older Mac, it’s time to either consider a hardware upgrade or you’ll be using HandBrake 0.9.4 for the rest of eternity.
Other Mac changes include VLC detection in both the /Applications and ~/Applications directories, a new Audio Panel supporting more than four audio tracks and support for multiple instances running simultaneously.
The update wasn’t accessible through the “Check for Updates” feature in version 0.9.4, so you’ll probably want to go to the HandBrake website and just download the installer in order to update.