I wrote a big part of my last book (my 8th) using IBM ViaVoice. The human interface is a bit clunky, but the software worked well for me, once I got used to it.

The challenge is that writing with my mouth seems to use different parts of my brain than writing with my fingers. It's a subtle difference, but I think the spoken stuff is livelier, fresher, more conversational. It does take some retraining, but ultimately I found it pleasant.

I am a pretty fast and comfortable typist, but speaking is considerably faster - even when I take into account the necessary editing that has to happen afterwards.

I never used DragonSpeak, the other leading speech-to-text product for the PC. I did use MacSpeak on a Mac (I may be misremembering the name; it was a couple of years ago) and found it not quite as good as ViaVoice on my PC.

Hope this helps!

Joel