Every so often, Plasma freezes on me or the graphics get cluttered. It is a hassle to restart KDE (logout/login) when you have 101 tabs open in Firefox and several xterm windows.
I had been a Gnome user since shifting to Ubuntu a couple years back, and recently shifted to Kubuntu/KDE when KDE 4.2 was released. Its been mostly stable, except for the occasional Plasma issues. Individual components in Gnome can be easily killed/restarted. For eg Gnome Panel can be killed/restarted using the following command.
killall gnome-panel; gnome-panel &
Now the same can be achived in KDE too. This is how you kill/restart Plasma.
kbuildsycoca4 && kquitapp plasma-desktop && kstart plasma-desktop
The above command can be run either through the terminal or krunner (kde run command).
No more restarting of KDE to clean up plasma mess. 
I upgraded to KDE 4.4 last week and its has been largely stable and amazing to work with. KDE is a much more powerful desktop shell than Gnome and I would recommend KDE 4.4 for everybody who use Gnome just because of a lack of better choice.
Thanks, that’s really helpful. I’ve found kde to be fairly unstable on my work desktop, but rock solid at home. In particular the plasma desktop occasionally crashes, but this will help me out with a simple restart. Cheers!
Tim