KDE or Gnome?
Developing KDE applications is pretty good using QT aswell, just the workings of QT-designer don't seem to gel as well with the actual back end coding as with Glade; QT-Designer doesn't have a 'Build' button as in Glade. However QT does seem to have a more straight forward (when coming from C/C++) object model, with classes fitting better, GTK however makes programming the UI easier using packaging. Where there might be a packaging implementation thing in QT, I've not really came across it; but if anyone knows, then let me!
Under KDE the PIM of choice is Kontact, which Gnome its Evolution. Kontact is a nice application with good interaction with the various peices of KDE such as Kopete etc, however Evolution can boast Exchange compatibility which is even better than that which Outlook provides! I know this because my work machine uses Outlook, and while its waiting to connect to the server to update calendars and emails, Evolution is sitting pretty telling me of new mail and syncing with my PocketPC! So for the time being its Evolution for me!
So for the time being I'm runnign KDE 3.5.1a with key apps being Kopete, Evolution, Firefox and Superkaramba.