I use Ubuntu 12.10 and I want to map the show-desktop keybinding to Super+d. I tried to configure it in Compiz configuration manager, in the system properties-keyboard configuration and in dconf-editor but without success. After each reboot the value of the dconf entry is reset to the default value <primary><super><d>.
I really don't know what to do now :P
I can recreate your problem in 12.10 if I change the setting through System Settings >> Keyboard >> Shortcuts.
This is probably related to Bug #936840 about the change in Gnome from using <ctrl> to using <primary>. Note that the setting in System Settings is given as Ctrl+Super+D, so the setting is probably no longer going through correctly.
When I left the setting in System Settings alone and made the change from CompizConfig or Dconf, the change held across reboots. Note that these two programs, use <Control><Primary><Super>d, so they apparently are able to hook the settings daemon correctly.
If you are still having trouble, try resetting System Settings to the default, rebooting, and then making the change from CompizConfig.
I know about the show desktop keybind (default Ctrl+Alt+D), which I use often enough. However, I'm looking for a way to minimize all windows without activating "show desktop".
I'm on a default install (i.e Gnome, Metacity & Compiz). I've looked through all the locations to configure keybinds, that I know. I've also looked at the default keybind list in the Ubuntu wiki and in the Compiz wiki. (Not to mention, searching here.)
I'm interested in knowing where it is available, if not in Gnome/Metacity/Compiz, or some other way to accomplish this with a keybind.
This person found a way to do what you are looking for: http://www.cs.bgu.ac.il/~gwiener/linux/minimizing-all-windows-in-gnome/
First install devilspie
Then create a file called minimize.ds in your home folder. In that file put the following:
Test it out by running: devilspie minimize.ds
If it works as it should then add a shortcut: System ➜ Preferences ➜ Keyboard Shortcuts.
Click on the Add button and fill in the fields as shown below, replacing YOURUSERNAME with your actual username.
And finally double-click where it says Disabled and press your shortcut keys.
It can be found in System--->Preferences--->Keyboard shortcuts
Try using wmctrl.
sudo apt-get install wmctrl
Then, create a new custom shortcut that executes the following command.
wmctrl -k on
This should do what you are looking for.
Ctrl+Alt+D? You can set it in Gnome System->Preferences
This is built into Ubuntu Settings.
Settings > System Settings > Shortcuts and Gestures > Global Keyboard Shortcuts > Select 'KWin' in KDE Component pull-down menu > Then scroll down to 'Show Desktop' > Assign a custom hotkey. Presto!