It was brought to our attention that the last version of OmniGrowl was improperly signed for Gatekeeper. This resulted in OS X throwing up a "damaged" error when trying to open it on some systems. It has now been properly signed, we very much believe. We're calling this version 4.5.5y3.
In other news, the royal we will be traveling from December 5 through January 7, so please forgive any delays in support responses during this time.