I've bound Win-R with the Run Application dialog in Metacity. However, the shortcut doesn't work when switched to Compiz. The entry Show the panel's "Run application" dialog box even doesn't appear in the Keyboard Shortcuts dialog in Compiz.
There are also other shortcuts that do not work in Compiz. I can add them using custom shortcuts, but I don't know the command line to popup the "Run Application" dialog.
Why are there so many shortcut entries missing in Compiz? (~90 entries in Metacity compared to ~20 entries in Compiz)
(OS: Debian Squeeze)
Screenshot: Keyboard shortcuts list in Compiz
As you see, the list is very limited, most shortcuts set in Metacity are missing.