I recently switched to using KDE 4, and I don't like that KDE uses so many of the Ctrl-Fn shortcut keys, since I use them for other purposes. Specifically, I'd like to disable the Ctrl-F4 shortcut in KDE. However, I have not been able to find this shortcut in System Settings -> Shortcuts and Gestures.UPDATE: Another shortcut I'd like to redefine is the Show window menu shortcut, which I like on Alt-Space, but which KDE has on Alt-F3. I have not been able to find a global place to change all shortcuts.
How to redefine kde4 keyboard shortcuts
kde;keyboard shortcuts
All of the global keyboard shortcuts are in Settings -> System Settings -> Shortcuts and Gestures -> Global Keyboard Shortcuts.  You'll probably need to go through each of the KDE components to find and remove the shortcuts you don't want.