Key features of KDE 4.8 include Qt Quick support in Plasma Workspaces, the re-written Dolphin file manager, KSecretService as a new shared password storage mechanism, and many performance and bug-fixes throughout the KDE stack.
Qt Quick in Plasma Workspaces is allowing for a standardized API implementation of widgets with native Plasma Look and Feel. The re-written Dolphin file manager is now faster, more scalable, and has a better visual interface.
More details on the availability of KDE 4.8 RC2 is available from dot.kde.org or the KDE.org press release.
The final release of KDE 4.8 is due out at the end of January.