Dvorak typists type faster (for example, the world's fastest typist uses Dvorak).
More logical design: Frequently used keys are on the home row of the keyboard. All the vowels are home row, left hand. 70% of all letters typed are on the home row of the Dvorak layout.
Efficient typing: you generally will type keys alternating between left and right hands. Only a few words require one-hand typing.
Increased Accuracy: your chance of missing a key or hitting the wrong key is much lower with Dvorak.