Under Snow Leopard, I had a couple of services set up to trigger Automator scripts for labeling files in the Finder. Cmd+Ctrl+Opt+9 applied orange and Cmd+Ctrl+Opt+0 applied red.
Upgraded to Mountain Lion (skipped Lion) and now Cmd+Ctrl+Opt+9 works but Cmd+Ctrl+Opt+0 doesn't. The latter is still listed in the preferences pane for services key bindings, but when I mash those keys all I get is a system beep. If I change the binding to some other key combination, it works. I tried switching it, using it a few times with the new shortcut, then switching back but no joy.