As for the ergonomic argument, it doesn't seem like the claims made (assuming they're true) have a huge effect on your health (again, you're almost never typing for a continued period of time). You might achieve 50% more key-hand alternation (is that metric even useful?), but when you're typing twenty words at a time, that doesn't come out to very many.
And in the end you have to deal with QWERTY anyway, every time you use a foreign computer.
That said, there's no real reason why QWERTY is intrinsically good either, other than that it's "good enough", and happens to be the standard.
In addition to that, a strong pragmatic point for sticking with QWERTY is that most keyboard shortcuts in editors and other tools are designed with QWERTY in mind.
As a Dvorak user, I came to this thread happy to discuss the pros and cons (I usually chime in on these threads). But it bothers me that the top the thread is someone who is so close-minded. Plus its obvious that you have never learned dvorak, so it also bothers me that you got any upvotes at all.
That said, I really do prefer typing in dvorak. You can feel the difference in number of off-home key presses -- it shows up in your wrists. The difference isn't subtle. "This is a test sentence" has 1 off-home keypress in dvorak and 13 in qwerty. This effect is pronounced enough that passwords, names with foreign spellings, and other types of entropic text are noticeably more awkward to type in dvorak (versus in qwerty, where all text "feels" roughly the same to type). Again, dvorak may not make much of an objective difference as far as health or WPM are concerned, but the feel is enough to make the inconvenience worth it to me.
EDIT: I see the post below me mentions keyboard shortcuts. They were the biggest sticking point for me and they remain the largest compatibility hassle when I have to use a qwerty computer. I would rate the frustration of having to think about shortcuts just slightly below the frustration of having to work with UIs that don't support emacs editing shortcuts, FWIW.
I typed on Sholes keyboards (and typewriters) since the 70s. My typing speed averaged between 135-170 words per minute in US English.
I attempted Dvorak for about a day but the layout is not good for a Unix user as some of the digraphs are pessimal.
When I switched to Colemak, I had a tremendous amount of difficulty undoing 35 years of various habits, good and bad. My first month, I probably averaged about 10wpm. I sent a lot of very short emails and was frequently frustrated.
Finally, my speed became "reasonable" and then I made an even more useful switch. Why bother with changing around the keys on keycaps that are still arranged as if they are driving levers through an inked ribbon onto paper? I looked for "matrix" keyboards and bought a Truly Ergonomic. Aligning the keys with my fingers, wrists, and forearms makes a lot more sense than continuing to follow old design constraints that are harmful for a large number of people.
Now I'm back to typing at a speed where I don't have to wait for words to appear on the page (any more than usual). It's much more comfortable and it's comfortable for a much longer period of time.
As for going to foreign computers, a) it's optimizing for the uncommon case, and b) Colemak is supported by almost every major OS and takes less than a minute to switch on Arch, Windows, or OS X. I do miss it on the iPhone or iPad on-screen keyboard, but it's supported on external keyboards.
 I'm not sure I'd buy it again as even the "silent" model is too loud for me. In addition, some of the punctuation keys are in annoyingly odd places and need to be remapped. A number of even more extreme ergo keyboards drop the staggered key layout as well.
I've known two people who repeatedly claimed typing speed doesn't matter - and they put their money where their mouths are! I'd be surprised if either could do even 50WPM.