Patch 3.1 General

All Ground Mounts may now swim without dismounting the rider. Flying Mounts still may NOT, and will dismount the rider upon entering water.
Ulduar is now available for limited testing. Please visit the Public Test Realms for more details. http://forums.worldofwarcraft.com/board.html?forumId=11572
Players level 40 and higher will now be able to visit their trainer to pay a one-time fee and access the dual talent specialization feature.
The achievement Brew of the Year has been removed from the Brewmaster meta-achievement. The achievement Brew of the Month has been added in its place.
A new Gear Manager feature has been added. Players will now be able to save gear sets for easy gear switching.
New high-resolution player textures for Northrend armor sets have been added. Players can enable this feature by setting Player Textures to High in the Effects Panel of the Video Options.
Players can now return items purchased with an alternate currency back to the original vendor within 2 hours of the purchase time for the original cost of the item. Stackable items (such as Frozen Orbs and gems) and charged items that can be purchased with an alternate currency are not eligible.
Confirmation boxes have been added to purchases over 150 gold.
The achievement Brew of the Year has been removed from the Brewmaster meta-achievement. The achievement Brew of the Month has been added in its place.
Noblegarden has been redesigned into a week-long holiday with new items, quests, and more. Various achievements have been added, including the meta-achievement Noble Gardener, which is now required for the meta-achievement What A Long, Strange Trip It's Been.
Applying a glyph no longer requires a Lexicon of Power. The same rules for switching between dual talent specializations now apply to switching glyphs and cannot be performed while in combat, Battlegrounds (except when Preparation is up), or Arenas (no exceptions). New - Build 9733
Copied Test Realm characters will no longer be copied with their achievement history in order to better facilitate the character copy process.

PvP

Arenas

Enemy Unit Frames: This feature is only available while in Arenas, with several options in the Interface Options.

Battlegrounds

Battleground quests "Concerted Efforts" (Alliance) and "For Great Honor" (Horde) now require an Alterac Valley Mark of Honor in addition to the current requirements. These quests now award more honor upon completion. New - Build 9733
Players will now be able to queue for battlegrounds from any location. Leaving a battleground will return you to the location from which you entered.
Seaforium Barrels can now be looted while mounted, seen from anywhere in the zone, and found at the Central Graveyard.
Teleporters can now be used while mounted and can now be seen from anywhere in the zone.

Alterac Valley

Drek'Thar, Vanndar Stormpike, the tower Heralds and Warmasters have received a hit point and damage upgrade in the level 80 version of Alterac Valley New - Build 9733

Strand of the Ancients

Capturing the Southern Graveyard will now automatically capture both the East and West Graveyards. New - Build 9733

Lake Wintergrasp

All players who attack a siege vehicle should now get credit if it is destroyed. New - Build 9733
Daily quests "Slay Them All!" (Horde) and "No Mercy for the Merciless" (Alliance) have had their PvP Kill requirements reduced to 10 from 20. NPCs defending the fortress and south towers now count toward these dailies as well. New - Build 9733
The number of NPCs defending the fortress has been increased. New - Build 9733
Siege Engines now have Steam Pressure as a resource type (replaces energy).
Siege Engines now have the Steam Rush ability from Ulduar.
The southern Siege Factories can be captured.
The time between battles will be saved should a realm shut down. If Wintergrasp is active when a realm shuts down, the game will restart from the beginning when the realm is once again live. New - Build 9733
Towers in Southern Wintergrasp now have more defensive cannons. New - Build 9733

Races: General

Command (Orc Racial): Applies to Shaman pets, and now correctly applies to Death Knight pets. New - Build 9733
Gift of the Naaru (Draenei Racial): The heal has been changed to an instant-cast direct heal instead of a heal-over-time.
Stoneform (Dwarf Racial): No longer makes you immune to poison, disease and bleed effects for 8 seconds. Instead, using Stoneform will clear those effects when cast. Cooldown reduced to 2 minutes from 3 minutes.