I switched to Dvorak three years ago. Mostly out of curiosity and because I heard it was better for my wrists.
One thing that I felt was really helpful was having different keyboards for the different layouts and not just a software switch. I started with a Typematrix and a year after bought myself a Kinesis Advantage. Both those keyboard have a grid layout (as opposed to the staggered layout of most standard keyboards). My experience (sample size of 1) was that this allowed me to have one muscle memory for the Dvorak/grid keyboards and one muscle memory for the Qwerty/staggered keyboard.
At the beginning, I was only using the Dvorak on the weekends and with some typing tutors for some exercise 10-20 minutes a day. I think I made the switch to Dvorak as my main driver after two-three months.
I haven't looked back since and still feel much less comfortable using Qwerty (only use it on the laptop which might play a role), although I can still touch-type on it quite easily.