I'm currently typing at a speed where I can physically feel that the layout of my keyboard is slowing me down. I've played with the idea of switching to DVORAK in the past, but the fears of major slowdown has kept me back.
Is the initial slowdown worth the long time gain?
The initial slowdown lasts only a few weeks if you work on your typing speed. When I first learned Dvorak I lost the ability to touch-type Qwerty, but within the first year I retrained myself and was able to switch back and forth (though I'm still not quite full speed on Qwerty). The only thing I can't do is use Vi keybindings in Qwerty. They seem to be in a different part of my muscle memory, which has never been retrained.