Although I am not fond of the K Desktop Environment (KDE) (I prefer Gnome), the new and/or improved features on the new version is worth a look.
This release includes a number of bugfixes for KHTML, Kate, the kicker, ksysguard and lots of other applications. Significant features include additional support for Compiz as a window manager with kicker, session management browser tabs for Akregator, templating for KMail messages, and new summary menus for Kontact making it easier to work with your appointments and to-do's. Translations continue as well, with Galician translations nearly doubling to 78%.
I am greatly interested in the KHTML branch since it is also used by Apple's WebKit and Nokia's latest WebKit-based web browsers that can be found in devices like my Nokia E61. :)
So, if you prefer KDE, upgrade now and take advantage of the new improvements.