Unfortunately, because Siri and voice dictation is so new but still considered beta so Apple is doing limited testing by only using 4s users. That limited testing of course is about 7 million users. I didn't really think I would be using it very much but since I got my iPhone 4 as I've been using it nonstop. I've actually stopped using the keyboard and occasionally will use this to type posts like this one on the Internet instead of actually typing.
I had a droid back when it first came out and it had voice dictation that was so horrible it was basically useless that's what I was afraid this would be. Fortunately that's not the case at all it works so well that I don't even see a need for a keyboard.
Like in this post, I can type entire chunks of text and never have to type a single keystroke. It's great it's like being able just talk and have your free flow thoughts appear on the screen. I use it for text messaging all the time I use it in the car I use it at home it's actually one of the greatest features that possibly could've added. I really hope that the entire operating system gets less and less visual and more and more intuitive.
I feel really sorry for the people that it's not working for. I really hope that they continue to get it better and better so it'll work for everybody.