NaturallySpeaking 9, coming out in August, claims to dramatically reduce the time it takes to model your voice, achieving the best-possible recognition soon after opening the box.
For some people, that best-possible recognition is said to be 99%. Maybe. I've probably gone throught the "voice training" process a dozen or more times over the years. Not only have I never achieved 99%, I've never achieved anything usable.
There are several factors: one is that "tethered to your computer, wearing a noise-cancelling headset, and watching the dictation in realtime," is not appealing to me. The second is that when you make a typo you are off by a coupe letters and then you get back on track. When a voice-reco system fails, the error mode is a parlor-game chain of semi-homonyms "wrecks a beach" == "recognize speech".
I'm ever optimistic, though. As a writer, I'd love to be able to do significant amounts of work using a digital recorder (PDA, smartphone, what-have-you) on the beach. I've even thought of trying out those lost-cost (human) transcription services. Maybe I'll give that a shot this National Novel Writing Month.