[Brian]

The first thing I'd probably try would be to set your preferences file aside and see if firing OmniFocus up and letting it create a new one helps.

You can do this by opening up
<your home folder>/Library/Preferences
and moving the file named
'com.omnigroup.OmniFocus.plist' to your desktop
(the last part may be hidden by the finder)

If you start OmniFocus now, does the app start successfully?

If not, let us know and we can gather more information about what's going on.