Bryan, had it been a while since you'd updated OmniFocus? Several versions back, we started requiring clipping shortcuts that incorporate the command key.
(Doing this works around a problem with how OS X handles service shortcuts that don't use that key. They would only work in a given application once the services menu had been clicked on.)
If you open up OmniFocus' clipping preferences, click on the keyboard shortcut field and then hit F19, you'll see that the shortcut that gets set is actually Command-F19. If you hit that shortcut, does it do what you expect?
If that doesn't resolve the issue you're having, the tips in
this thread may help; you can also feel free to email the
support ninjas - they'll be happy to help.