I always used gnome, because all the apps i used were gtk. However, recently I have found features in qt based apps that made them worth while. For example amorak vs rythmbox, the multiple backends and equalizer made it worth it to switch. Another example is kmplayer, it fits nicely into a kde desktop, and can run different backends for different things. With ubuntu there is no option for this, you can't have totem xine and totem gstreamer installed. So you need totem, mplayer, and xine installed 3 apps, 1 to test gstreamer's growing support, one for my web browser plugin (nothing works as well as mplayer for that) and xine for dvd support and weird codec support (xine seems to do both better then mplayer). So I figured I'd install kde with my newest install of debian.
I have to say I'm hooked. Debian's kde is much cleaner then kubuntu, which had many things I did not like and made a lot of changes I had to spend time undoing to get my system the way I liked it. KDE runs just as fast as my old gnome setup, and everything blends nicely into my desktop. I'm using amorak, kmplayer, quantra, kate, konq, etc all without even missing the gnome replacements for these apps. I have also found the kio slaves make my life a lot easier in both programing and functionality. They work a lot more intuitively then the gnome vfs. I still have a few gtk apps I can't live without, like bluefish. But 99% of the apps I use for work, and for fun have kde versions that are just as good or better then the gtk apps. I have found I really love kontact and kmail. I like it more then evolution, and thunderbird has never really met my needs. Of course I can never get away from firefox, it is still needed for a few websites konq just can not render properly. I do not use open office, I usually just use abiword and Gnumeric. However I switched to koffice, and found it works perfectly for my needs.