I'm not sure whether this is possible within the limits of the UI framework, but it would be nice to have a checkmark in the plugins menu next to each enabled plugin.
My thought is that the OS X interface allows for a checkmark to indicate whether a particular toggle is enabled and this feature could be used on the plugins menu to show which plugins are enabled/disabled. Obviously, this information is also available on the Manage Plugins dialog, but the convenience of being able to quickly open and close the plugins menu would be nice.