I've got htns mapped to the direction keys, too, and it works great. I think it's even easier than qwerty's direction keys because you don't have to move your right hand at all; you have to move the forefinger left to hit 'h' on qwerty. It's a happy coincidence that the 'unmapped' keys aren't used very much, except for 'n' and you can remap that to the Dvorak j, k, or l.
Playing QWOP is impossible on Dvorak, however.