Hi.
I tried switching to the dvorak layout about a year ago, but abandoned the effort. The undisputed advantage of the
Dvorak Simplified Keyboard is of course the speed and comfort of typing, since you don't have to move your fingers as far/often as with QWERTY (which was designed with the keys far apart to prevent jamming of older typewriters), but you probably already knew that.
The real show stopper for me was to re-learn. I've been touch typing for... oh, almost 8 years now (I'm 21), so it was almost impossible to re-wire my muscle-memory to hit the right keys.
Using the layout wasn't all that important to me, because I'm a fast typist already, and when I considered the other difficulties involved (mentally switching between the two layouts, switching the layout on the machines I use - not as trivial as it sounds, finding a way to type German umlauts) I decided it was not worth it.
However, I've read accounts from people who actually made the switch and pretty much all of them are pleased; they usually retain their ability to type in QWERTY, although IIRC at slightly slower pace.
Heh. I guess what I wanted to say is that you'll have to try out for yourself, because it's probably different for everyone.
Edit: Sorry, I misread your initial question.
If you don't know how to touch type yet, learning to do so definitively pays off, and allegedly it is easier to learn Dvorak than QWERTY. However, the other criticisms are still valid; to get a better picture you might want to have a look at the material linked at the end of the Wikipedia article.