I switched to Dvorak a while ago. I didn't notice any particular typing speed-up; in fact, I may be slower in Dvorak than Qwerty right now! I don't think typing speed is an important factor to consider when choosing Dvorak: it hasn't made a difference for me, and I don't find it that important when programming. The real gains for me is in ease-of-use, where Dvorak excels.
Dvorak is significantly easier on the hands than Qwerty. When not using a program which relies on Vi-keys, Dvorak is by far preferable, even with the arguably worse-placed brackets. As advertised, I much more rarely have to move my hands from the home row. If you are at all concerned about the stress you put on your hands, or if you find it tiring to type quickly in Qwerty, you ought to try Dvorak.
It seems infeasible to use Vim with Dvorak. Right now, I use Qwerty in a terminal and Dvorak elsewhere. I've gotten very good at switching between layouts, so it's not a problem for me to switch between computers (as was mentioned as a problem in another comment) or switch layouts on the computer. To use Vim with Dvorak, the recommended solution seems to be to set Vim's keymap so that it acts like Qwerty in normal mode and Dvorak in insert mode. Despite being able to switch between layouts regularly, switching every few seconds was too jarring for me to continue with it. If you use Vim, I would not bother with Dvorak.
Dvorak has a significant learning curve. It probably took me a week or so to be able to touch-type with it, and then maybe three more to touch-type effectively (but this was a long time ago! so it is likely that I am misremembering). If you are unable to commit to the lost productivity, I wouldn't worry about it. However, if you are able to spend the time, it will be a valuable investment which should make up for itself in a couple of months.