Okay, so I won't make any spoilers for anyone, but in the recent GSL (Global Starcraft League for those who are new), ST_July, a Zerg player, used constant and early aggression to beat both Terran and Protoss players. Specifically, he massed roach against an early-expanding Protoss on a large map, and Baneling-busted through a Barracks wall on another map.
Mind you, his micro and timings are perfect. He can afford to throw large masses of units against his opponent, knowing that he'll either have time to build defenses if his attack fails and there is a counterattack, or he knows how to avoid forcefields (in the case of Protoss opponents).
However, in the most recent championships, MC totally dominated all opponents by clever use of force fields, but I don't blame July for his loss, there - he was simply outplayed and outmaneuvered.