Mac OSX actually has voice control but the little round window is weird and it unexpectedly quits quite lot. Oh and the knock knock Jokes aren't funny.
But the cool thing is that it can guess unknown words pretty well. Leopard's speech engine is quite good actually. I made an entire book into an mp3 (using automator) and listen to it on the iPod. Very creepy at first, but you get used to the Alex voice telling you a story. The voice may seem unfittingly enthousiastic at times though.
Example:
- Tell me the truth. She died, right?

- YES!!!



I am sorry for your loss.