Dvorak is an optimized keyboard layout designed to help reduce the movement of the users fingers resulting in increased typing speed and a reduced strain on the fingers preventing repetitive strain injury.
Computer keyboards do not have the constraints QWERTY typewriters once had, therefore Dvorak was made in 1936 by Dr August Dvorak in order to be the most effective layout. Typewriters had to have a layout as such to prevent the hammers from jamming when a typist was typing quickly, thus common keys were at opposite sides of the keyboard.
I started using Dvorak as my primary keyboard layout in 2003, and learned it on a qwerty keyboard without rearranging the keys to force myself straight into touch typing (which is still how I type today). However, as a programmer, I have noticed some very awkward combinations when doing anything other then what typewriters were originally designed for, ie not typing words.
First off, you notice it is not optimized for the web. Typing ‘.’ with the ‘www.’ and ‘.com’, ‘.co.uk’ and ‘@’ symbol is a little awkward, but is still not worth worrying about. Cut, Copy and Paste, ‘x’, ‘c’, ‘v’ are all over the place, so having cut and paste as ‘x’ and ‘v’ become a little meaningless, and you do start to get concerned over pressing ‘ctrl-w’ instead of ‘ctrl-v’ by mistake, which is close window, followed by a lot of annoying retyping or navigation in a browser.
Secondly, as a coder, you notice that certain symbol combinations are actually slow to type, and permanently needs the shift key to be pressed/released causing mega slowness. (However is that much different from qwerty?)
Programmer Dvorak helps the second point, converting the top number row to be primarily symbols, with numbers available with the shift key, ordered in odds on the left, evens on the right (the originally Dvorak layout). This is available as an additional driver for windows, linux and mac.