The Mists of Pandaria systems patch will be going live this week and it brings a lot of changes! Make sure your Background Downloader has downloaded the files so you aren't stuck waiting.
New Talent System - Now has 3 talents per tier, with 6 tiers.
Class Changes - List of class changes and short overview guides.
New Ability Animations - So shiny!
Experience Required to Level Changed - Reduced amount of XP to level to 85
11th Character Slot - Unclear if it is coming in 5.0.4, but it will be
AoE Looting - Loot all of the corpses in an area around you with one click!
Scarlet Monastery and Scholomance Revamp - New lower level versions of the
Dungeon and Raid Valor Reward Changes and Currency Conversion
Account Wide Achievements, Mounts, and Pets
Simplified Buff and Debuff System
Item and Stats Changes - Changes to expertise, Spell resistance, Resilience
New Druid Forms - Armored forms for Incarnation and a new Travel Form.
New Warlock Pets and Emotes
Cross-Realm Zones - Play with friends on other realms, no more empty wor
Interface Changes - New and easier to use interfaces, loot history, and more$