The author complains that his QWERTY muscle memory went away when learning Dvorak. This doesn't match my experience. I can still use QWERTY, somewhat slower than before I learned Dvorak, but not much, and since I use Dvorak 99% of the time, it's no big deal.
This matches my experience. I automatically switch to QWERTY when I use someone else's computer, to the point where I get confused when I use the computer of one of my colleagues that also uses Dvorak.
If you set up some shortcuts to switch between layouts then other people using your computer is not a problem either.
The hardest I find is when i use the keyboard of someone else I know who happens to use Dvorak, there is about a minute of wtf dude... sometimes even if I know they use Dvorak!!
It's also a great party trick. I once lent my computer to my daugther and her buddy, it was kind weird for them that no keys matched up, but even weirder when I showed them I could easily switch between the two. They were so sure I wouldn't be able to type with qwerty.
Their faces at that point were priceless :)
This is also my experience after about 10 years of Dvorak and I work on other people's computers in QWERTY daily.
I will sometimes begin to type in Dvorak unconsciously if I am on a laptop keyboard that feels similar to my personal laptop.
As soon as I see the mistaken letters coming out I switch back without any effort.
