KDE SC 4.9 will be officially released at the start of August, or so is planned, but for now the developers are hoping you can test out their latest RC-phase packages. This second release candidate is just about polishing new and existing functionality while addressing any other outstanding bugs.
Among the features of the KDE 4.9 desktop is Qt Quick support within Plasma Workspaces, the Dolphin file manager has seen many improvements, deeper integration of Activities, and many performance improvements along with the usual platter of bug-fixes.
The release announcement for KDE 4.9 RC2 is available at KDE.org. At KDE TechBase is more about the KDE 4.9 feature set.