World of Warcraft patch 5.4 will be introducing a new feature called Proving Grounds that will allow level 90 players to test their abilities at being super good at this game. Essentially, these challenges are instances in which players can choose which combat role in the holy trinity they want to play and then face scenarios geared toward testing their skill in that role.
Gear will be scaled to the level of the challenge, because it's purely a skill evaluation. Scenarios will be different depending on your role; if you're damage then you're alone and must take out foes quickly, if you're a tank you'll have to hold aggro while your NPC companion does the dirty work, and if you're a healer then you'll have to keep a party alive during a battle. There are four tiers of difficulty, and you'll have to progress through them in order. The highest level will consist of you trying to last as long as you can, and there will be leaderboards and such for that. Also, achievements. More details here.