I picked up Dragon about a month ago, but I haven't quite taken the plunge in using it for writing fiction. I use it for writing emails, and for writing this post. :-) It did take a while to get used to dictating with it, but I found it saves me a tough time with my freelance work. I'm a business copywriter, and it's pretty easy for me to dictate drier nonfiction stuff like that.
I would agree with the previous commentor that using it for plotting and other places where you don't need as much flow would be a great way to learn. I'm excited to use it to start writing fiction, because it's saved me so much time doing freelance work. Now that I've mastered that, I feel like I'd be able to master dictating fiction.
It can be a little bit buggy – or at least it is on my Mac – but it's word recognition rate for me is almost perfect, even after only a month of using it. I think it's worth the plunge – but the learning curve is pretty steep.