I've been practicing dvorak for about a month. Not much since I got above 10wpm(1 hour a day for a week), but I've used it when there has been typing to be done. I've gotten to 40wpm, and I started with 70wpm qwerty speed. Incidentally, I've also forgotten how to type with qwerty.

I'd suggest you find a week when you are free to use about an hour of your time every day to practice dvorak and don't need to type anything really, and then maybe another week when you are not under any stress about your typing speed. After that, you should be able to type well enough to cope, but its gonna take more time than that to get even faster. If you know some systematic touch typing systems already, and know how to use them, i think you might be able to retain your qwerty ability. I lost that because my touch type system for qwerty was so wild and unorganized, and learning this more proper style pretty much overwrote that. Also, knowing these proper touch type systems probably help you learn dvorak faster.