I think again, as some have said, that part of the speed boost is due to learning proper typing, but the less movement also means less error to me. Some little things like learning to use the alternate hand for shift (Stamina 2.5) help typing, but not in 10FF, considering the few amount of capital words.
I can't imagine that anyone would still remember QWERTY. I've used Dvorak for 9 months or so, speed has gone from a best of 90 Qwerty to 143 Dvorak. There seemed nothing incredibly pressing besides chatting requiring great typing speed, so I immediately went cold turkey and did lots of practice while I was being driven around (generally half an hour or so a day on Stamina).
And best of luck on your transition! I am sure that you won't regret it. For all those who have issues with using Dvorak on a public computer without being able to change the settings, I personally have downloaded DVAssist to my USB which I carry in my wallet (it's a novelty flat USB) and can activate that, which completely converts everything to Dvorak.