While test releases of NetworkManager 0.9 have been available, this is a major new release that "hugely" simplifies the configuration model of network devices for both users and delivers. "The most significant feature for users will be richer and more capable network control and configuration applets for GNOME 3.0's GNOME Shell and Ubuntu's Indicator system." This work ends up simplifying the D-Bus API too, for easing developer adoption.
NetworkManager 0.9 also now supports fast user switching and has better support for shared computing.
There's a lot of changes that can be found out by examining the NetworkManager Git log.
The release announcement on the NetworkManager GNOME.org project page simply says:
ROCK ON: this new stable release includes a ton of great changes for users and app developers, like Fast User Switching support, simplified configuration, more flexible API for new network applets, and more. Check with your distro of choice for updates, or grab NetworkManager and nm-applet for great networking flavor!
Those wanting to fetch the NetworkManager source can grab it from the FTP mirror.