You may have noticed that OS X's Character Palette can be out-of-date regarding the script and character names in the latest version of Unicode. That's because Apple apparently only updates this data in the named OS X releases. The last updates of Tiger, from 2007, still use the data from Unicode 4.0 of 2003. The most recent update of Leopard, from September 2008, has data from Unicode 5.0 of mid-2006.
This does not matter much in practical terms, however. Both Tiger and Leopard, with appropriate fonts installed, seem able to input and display all scripts and characters included in Unicode 5.1 of April, 2008.