[Greg Jones]

You can create the following script:

tell application "System Events" to ¬
	set visible of first application process ¬
		whose frontmost is true to false

Save the script to ~/Library/Scripts/Applications/OmniFocus

Then you can add the script to your OmniFocus toolbar and you'll be able to hide the window(s) in OmniFocus. Switch back to OmniFocus and the window(s) will be restored to the unhidden state.

As an alternative, you could save the script to "Your Computer HD name/Library/Scripts" and it will be available to all your applications from the Script Menu in the Menu Bar., but then you cannot include it in your OmniFocus toolbar unless you also save a copy in the above-mentioned OmniFocus directory.