Minecraft wiki entry for Frostburn_Update, associated text: /tp command y-coordinate range increased.
Several minor changes to world generation.
Structure blocks can now be used in-game.
Chorus fruit and ender pearls now teleport players from ride-able horses / pigs.
Mobs can now shoot while they are in a boat.
Endermen now spawn in the Nether.
Magma cubes now spawn about twice as often.
Skeletons now shoot the arrow they are holding in their off-hand.
Wolves no longer despawn.