When the user double-clicks on a document file in the Finder, OSX doesn't simply give the filename as a command-line argument when calling Blender, as it is done in other OSes. Instead, it launches the app if needed, and then sends an "openFile" event. The user can also open a document file by dropping its icon on the app dock icon. But as this is not real Drag'n'drop, I've renamed the Ghost event to a less confusing "GHOST_kEventOpenMainFile" name. DND Ghost wiki page updated : http://wiki.blender.org/index.php/BlenderDev/Blender2.5/DragnDrop