Worn haste does not stack with other worn haste. You will only benefit from the highest worn haste. Worn haste does stack with spell and song haste though.
Cool, first post! Anyway, in case anyone was wondering, Haste is how quickly you get to attack an opponent. The higher your haste, the faster you'll be able to attack. It may even get to the point where you could get twice as many hits in as you normally would.