[jasong]

Thanks to both of you; alas no luck. I've done both of your suggestions, and I'm still unable to assign command-space to OmniFocus.

If I have Spotlight set to command-space, and try to set it in OF, the Spotlight menu shows up, and nothing happens in OF.

If I uncheck the Spotlight option in preferences, and try to set it in OF, I get the error that I can't set it.

If no one has any other thoughts, I'll submit as a bug to the ninjas.