the thing is, it doesn't make you forget how to do QWERTY. it's just an alternative.
Well, since you're just learning dvorak, a good experiment would be to get some kind of typing software that tests your current WPM and then try again after learning and using dvorak only for a while.
I don't really understand how having a different look to the keyboard matters. if your friend had a Dvorak keyboard, couldn't the person have figured out that the letters were in different places? Or was the issue that it was a normal keyboard, but the computer was set to dvorak?
"I'm pressing W, but it keeps printing a B on screen!"
Anyway, the thing is, the utility of me learning dvorak has no relation to other people's use of it. Other people's keyboard usage does not effect mine. Even if I were the only person in the world to use it, it would still be a benefit to me-- so I really don't see the problem.
There is no problem as long as you always only ever use your own PC. Me, I can pretty much use any PC in the world and have no problem typing something. You'd have a bit of a hard time finding a keyboard with a dvorak layout.
And what benefit is there over Qwerty? If you already know how to touch-type on a QWERTY layout how is Dvorak faster?
Also, carpal tunnel comes from repetitive stress. Switching keyboard layouts will just change the location of the repetition. The best way to avoid carpal tunnel is to take frequent breaks when typing, and to assume correct typing posture so as to avoid injury.