We tried Dragon naturally speaking about 3 years ago in our offices. The Boss wanted it to work (it was his pet project for years) and was disappointed because he got laughed out of it by everyone else. Complete gibberish was typed up.
We had our IT person review it at the time and the consenus was that this type of software is "almost there", but not quite. As I said, that was about three years ago, so perhaps it has improved.