Because those guys at Blizzard have a wonderful sense of humor as well as an unerring knack of dangling the right carrots in front of players' proverbial horses, they've come up with the most adorable little pet to entice everyone to try out the new dungeon system to be implemented in patch 3.3. Called the Perky Pug, this elusive and adorable little fellow is rewarded to players who group with other random players using the new dungeon system. According to the patch notes, "the more random players with whom one groups, the faster the pet can be obtained."
That means the process can actually be pretty painful. It's kind of like playing Russian Roulette, except that instead of one bullet, you can possibly have four. And instead of bullets you have inept, or badly geared, or socially abrasive (or combinations of all three) players. And instead of your head, it's your... well, okay, it's still your head that can get pretty messed up.