The previous so called “Spaces” are now part of “Mission Control” in Mac OS X 10.7 Lion. It implements multiple work spaces as known from common Linux desktop environments.
Unfortunately it grabs the global keyboard shortcuts Ctrl-1, Ctrl-2, …, Ctrl-0 and Ctrl-Option-1, Ctrl-Option-2, …, Ctrl-Option-6 to switch to the corresponding space by default. This prevents using any of these shortcuts in an application. I had defined some of those for use with my favorite editor vim, where the shortcuts ceased to work after the upgrade to Lion.
Even more unfortunate, it’s a tedious task to stop Mission Control from allocating these keyboard shortcuts. The GUI offers the configuration check boxes only for spaces which are currently enabled.
So the solution was to enable all possible spaces, which are capped at a maximum of 16, using the Mission Control interface. Then disable the check box for each of them in System Preferences > Keyboard > Keyboard Shortcuts.
As said a tedious task, but works. I was hoping to provide some defaults write command here, but I was unable to determine where these settings are stored.