Tibetan: This is the primary new script included with Leopard, covered by the fonts KaiLasa and Kokonor, with 3 input methods provided.
Georgian: Included in the newly-added (but actually old) Windows Arial Unicode font. (This also contains Bengali, Oriya, Telugu, Kannada, Malayam, and Lao, but Leopard has been programmed to ignore them, perhaps because they would not display correctly.)
Shavian: Apple Symbols now has this in addition to Deseret.
No keyboard layout has been provided for Georgian, Shavian, or Deseret.
Reflecting the new Russian and Polish OS localizations, the number of fonts which include Cyrillic and the Latin characters needed for Polish has been significantly increased, and includes Marker Felt and Hoefler text among others.
Scripts included in Unicode 5.0 but for which users will still have to download fonts from other sources are N'ko, Phoenician, Balinese, Phags-Pa, Sumero-Akkadian Cuneiform, Buginese, Glagolitic, Coptic, Tifinagh, Syloti Nagri, Old Persian, Kharoshthi, New Tai Lue, Limbu, Tai Le, Linear B, Cypriot, Ugaritic, Osmanya, Tagalog, Hanunoo, Buhid, Tagbanwa, Old Italic, Gothic, Syriac, Thaana, Sinhala, Myanmar, Ethiopic, Ogham, Runic, Khmer, Mongolian, Bengali, Oriya, Telugu, Kannada, Malayam, Lao.
Here is some info on script support in Windows, which does include a number of those still missing from OS X.