Available in Patch 4.0.1 In Cataclysm, classes with secondary resources (resources other than energy, mana, and rage) will receive a second, customized resource bar to keep track on that resource. Death Knights already have one for their runes, but three other classes will be joining the team as well:
Available in Patch 4.0.1 In addition to the secondary resource bars, those of you familiar with addons like Power Auras will notice that some of their talents and class mechanics force different images to flash around the character whenever certain talents proc. For example, Retribution Paladins will see their Mastery popping; Marksmanship Hunters will see and so on.
Available in Patch 4.0.1 The spellbook has also got a nice makeover. Besides now only having one rank of each spell/ability, it also displays at which levels your future abilities can be learned. A nice addition is the guild perks tab below the general and the three specs' abilities, where your perks can be inspected. Aside from that, mounts and companions have been moved to a separate tab at the bottom of the window, where they will be displayed in a modelviewer. Professions are no longer listed under your general tab in the spellbook but have moved to their own tab inside of the spellbook. Inside you will find all your professions, with progress bars for the skill level and any specializations if you have one. Each profession will have all of its relevant spells linked to it (e.g. Jewelcrafting will have Jewelcrafting and Prospecting).
Available in Patch 4.0.1 The glyph pane is now longer in the character window but in the talent window. Glyphs still need to be purchased as consumable items, but they can now be learned, effectively relieving you of the need to re-purchase unlearned ones! Learned glyphs can be selected from the list to the right, and applied. A major change is the addition of prime glyphs, raising the total number of slots to nine.
Available in Patch 4.0.1 The Tradeskill window has also received a lot of loving with this expansion. Besides things being moved around to make more "sense", a few extra filters have been added—such as the "has skill up" filter which obviously shows you all your craftables with skill ups!
Available in Patch 4.0.1 Another revamped window, staying in theme with all of the other changes, is the Trainer Window. Now that there's only one rank for all the abilities, this was a much needed change. The changes here are mostly visual.
Available in Patch 4.0.1 The changes to honor and arena points, along with the new battlegrounds made way for some rather sexy changes to the PvP window. With separate tabs showing all your battleground and arena team info, it will be your one stop shop for all your PvP needs.
Partially available in Patch 4.0.1 The guild UI has been vastly improved. The roster now consists of three panels, selectable through a dropdown menu: player status, guild status, and professions. The last one is a new addition that lets you view other guild members' professions, and their recipes. The main guild tab has been updated to display guild events and guild news, along with the brand-new guild perks that your guild has achieved! Guild controls and information also have been made more streamlined.
Available in Patch 4.0.1 The minimap has also received a few changes, the first of which is the ability to track multiple items! No longer shall you have to decide between looking for fish or finding that elusive Frost Lotus. The other is an addition anyone who has ever used QuestHelper will enjoy: there is now a minimap arrow that will direct you torwards the next objective if you use the ingame quest objectives. Elite monsters that are objectives of group quests will now be marked with a skull on the minimap which lets you also track their movement.