I never learned to touch-type in QWERTY. I taught myself Dvorak when I was in grad school, using Mavis Beacon. My DH also types on Dvorak, although he can touch-type QWERTY. In fact, early in our relationship, when we were using UNIX 'talk' to teletype to each other, he correctly deduced that I was a Dvorak typist from watching my errors.
It made a huge difference in my speed, of course, since I wasn't touch-typing before. I think I generally type around 70-80 WPM now. My husband is significantly faster than I am, and I think he saw about a 30-50% increase in speed from Dvorak.
I didn't learn it because of speed, but because of incipient RSI. I figured I should start with the keyboard that was going to put the least strain on my hands. Aside from the fact that the IT guys freak out whenever they have to do something on my computer and the keyboard doesn't work like they expect it to, I have no problems with it - I really like it. And I've never developed a serious RSI problem, even in grad school when I was programming all day a lot of the time.
Being able to do only one keyboard has occasionally been limiting for me, but it's not a huge problem. The biggest difficulty was when I needed a typewriter that could type Dvorak but did not have a memory for my Washington bar exam. I found one on ebay from a university supply room that was being liquidated. (It did have a memory, but it was removable, so I just showed up for the exam without it - no problem.) I would like to be able to touch-type it QWERTY, too, but not enough to put in the time to learn it.
