One of the big UI changes coming in patch 3.3 is an option to Consolidate Buffs. It appears that when the feature is enabled, specific short term buffs like Replenishment and longer duration buffs like Gift of the Wild or Arcane Brilliance will be tucked aside and hidden in a buff box. When you mouse over it, the box will expand and display the buffs within. In other words, we can get more real estate back!
On the other hand, certain important buffs that may be critical to the operation of your class will always be displayed. For example, Art of War procs on my retribution paladin will always show up so I know when to slam Exorcism. (Don't hate on me because I have ret paladin now!) Heroism (or Bloodlust) and other similar cooldowns will be shown as well as range limited buffs like totems and paladin auras.
From the debuff side of things, there's another option called Castable Debuffs. When it's enabled, all it will do is show debuffs that you apply. My elemental shaman will throw Flame Shocks and that's all that will appear. I won't see a shadow priest's Misery or a rogue's Rupture. It's an interesting way to cut down on screen clutter.
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to the Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.