Theming one's OS to look like a Mac is all the rage these days, but for the most part such modifications are superficial. However, Global Menu actually changes the user experience quite a bit. For those who haven't seen a Mac before, [do such people exist?] on Mac OS, the menu for applications is located in a bar at the top of the screen, rather than the top of the window, like in Windows and Gnome.
With Global Menu, and a simple GTK hack, one can get the same interface on GNOME. It lets you use their computer differently, and yes, it makes your OSX themes more authentic. We've been using it for about three weeks now, and it is pretty nice. It all comes down to the individual's preferences, and that's what Linux is about, after all.
