Soon you may be able to execute Gnome/Gtk+ based programs
NATIVELLY NATIVELY on Quartz without the X11 Emulation.
Someone (thanks to exist) is working on the porting.
It may be the incipit of a new era for Open Source software on MacOSX. Take a look at this.
One of the most interesting characteristics of Gnome-oriented applications is the coherence between the HIG (Human Interface Guidelines) of Gnome and MacOSX.