Looks like GTK# (and the underlying Gtk+), as well as MonoDevelop, have gotten a boost for Mac users:
http://blog.xamarin.com/2012/04/03/monodevelop-updates/
Don't forget that after upgrading Mono, you have to reinstall Cobra.
If anyone is interested in doing a Cobra add-on for MonoDevelop, let me know. MonoDevelop runs on Mac, Linux and Windows.
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