While Zeitgeist began as a logging and activity engine for the GNOME Desktop as part of the GNOME 3.0 work, last year it was announced that Zeitgeist would be coming to KDE too as part of cross-desktop collaboration. The Zeitgeist support in the Phonon library allows multimedia applications to add playback activity to Zeitgeist. This is part of the GNOME and KDE's mission of more semantic desktop capabilities.
Phonon 4.5.0 also features integration support with Qt Designer and the Phonon API now also supports the DVD menu button. There's also various other smaller improvements and bug fixes.
Read more in this blog announcement.