Keith, xmas was talking about the left-hand portion of the "Keyboard Shortcuts" tab of the "Keyboard" pane of System preferences.
If you select "Services" in the list you see there, and scroll down a bit, do you see "OmniFocus: Send To Inbox" in the "Text" section of the list on the right-hand side?
If you select "Services" in the list you see there, and scroll down a bit, do you see "OmniFocus: Send To Inbox" in the "Text" section of the list on the right-hand side?