The advantage of being able to use any machine at close to your normal typing speed is pretty clear.

Many Dvorak typists type QWERTY at high speed, but not without looking at the keys. Most QWERTY keyboards have the advantage of having the symbols printed on the keys :)

For those who switch computers all the time, and use more than just a few boxes, Dvorak is annoying. But if you, like me, use your own box for more than 90% of the time, consider this: 90% comfort versus 100% discomfort.

By the way, KDE and Windows make switching between two layouts very easy. Sysadmins really have no good reason for disallowing Dvorak.

Especially if you are a professional programmer and don't have specific medical reasons for avoiding Qwerty keyboards.

Your statement is very dangerous and I hope you will take it back. It is very important to do everything to AVOID those medical reasons. I had one year of sitting at home, doing nothing (hands are needed for almost everything), having huge medical bills and no income. Dvorak is free and easy to learn (With http://www.dvorak.nl/, you can learn to touch type Dvorak in less than 10 hours), and I think everyone who uses "I don't have RSI yet" as an excuse to not have to go through the learning phase is a stupid idiot and *deserves* the pain thousands of others have already experienced.

... then you are at a competitive disadvantage if you move from job to job.

I will not ever work full time for someone who forces me to use QWERTY. Employers who do not respect health will have to search harder for people. More and more people demand healthy work places, and it won't be long before employers can get only the worst of coders to work for them.

I can just imagine how much worse it would be if I didnt use a Qwerty variant.

Your imagination is fooling you. QWERTY and QWERTY and QWERTY and QWERTZ and AZERTY are very similar, which makes switching hard. Dvorak is different enough to make switching and knowing you're using the wrong layout much easier.