As noticed by the good folks at the Kōyasan Daigaku Inseikai 高野山大学院生会 weblog, the newest version of Mac OS X contains built-in Tibetan fonts and Tibetan keyboards. This image shows some text typed in using the Wylie keyboard: to type in gzhan, type "g-z-h-a-n." It is the easiest system for typing Tibetan I have seen on the Mac. The OS also offers Tibetan-Otani and Tibetan-QWERTY keyboards.
If you are a scholar who needs to type in Tibetan, the new OS X may be worth it just for this feature.