I switched to Dvorak about 15 years ago. I agree with others here: I switched from being a Qwerty typist with poor form, to a "correct" Dvorak typist. In the end I'm a pretty speedy typist (~130 wpm), but I can still Qwerty well enough that it isn't painful.

However, I think the speed-up can mostly be attributed to forcing me to have a clean slate and learn to type correctly, rather than any intrinsic advantage of Dvorak. On Qwerty I typed the style I'd evolved since elementary school, and on Dvorak I touch-type like I'm meant to.