* Portals in Dalaran/Shattrath Removed
* Class trainers in Dalaran where portals once were
* New race-class combinations (excluding worgen/goblin)
* New Gnome/Troll starting areas
* Changes to existing zones
* New cata load screens
* New cata intro cinematic
* New cata login screen
* New music
* City Quartermasters, with rep tabards
* Bug fixes
* Class balancing
* Druids, paladins, priests, and shaman will have their talent trees reset
* Experience required to gain levels 71 through 80 is being reduced by 20%
* New tamable hunter pets (Monkey, fox, dog, and beetle, as well as new skins for existing pet classes.)

* Creating worgen/goblin characters
* Worgen/Goblin start zones
* Archeology
* Professions past 450 (Illustrious Grand Master)
* Guild leveling
* Guild achievements
* Eastern Kingdoms/Kalimdor flight
* New Zones (80+)

Mounts and Items Removed in 4.0.3

Originally Posted by Lylirra (Source)

As stated in the Under Dev page (http://www.worldofwarcraft.com/info/underdev/), patch 4.0.3 brings about The Shattering, a cataclysmic event that will forever change the face of Azeroth. As we prepare to raise the level cap and introduce two new races with the Cataclysm expansion, it's important to keep in mind that the game world is going through tremendous changes that will affect the availability of certain rare mounts and items.

Swift Zulian Tiger

Zul'Gurub is changing from a raid to a leveling zone in 4.0.3, and this mount will no longer be obtainable.

Swift Razzashi Raptor

This mount will also no longer be obtainable after the change to Zul'Gurub.

Razzashi Hatchling

With the change to Zul'Gurub this non-combat pet will no longer be obtainable. (Update - The Razzashi Hatchling is still obtainable in Patch 4.0.3a)

Tome of Polymorph: Turtle Mage

This tome will continue to be available through other means.

Crusader's White/Black Warhorse and Swift Alliance Steed/Swift Horde Wolf

As the attempt-based tribute system is being removed from Heroic Trial of the Crusader, the Argent Crusade Tribute Chest will no longer spawn, and these mounts will no longer be obtainable

Reins of the Blue Drake

This mount will once again be available from defeating 10-player Malygos without needing to use the Dungeon Finder. The Reins of the Azure Drake will only be available on 25-player Malygos.

Mimiron's Head

This mount will change to be a very low drop chance when defeating 25-player Yogg'Saron with no Keepers assisting you

Invincible

This mount will change to be a very low drop chance when defeating Heroic 25-player Lich King

Although we have no current plans to introduce new ways to obtain the Zul'Gurub mounts, pets, and the tribute mounts, they may return should we find a place where they fit in the future.