We use it for work for live subtitling and it's okay with some things, others not so much. Like some others have said, it needs training - basically the more you use it, the better it gets, especially the newer version 11, it's much improved on 10, in our experience here. We've found that ambient noise isn't as much of a problem as Dragon makes it out to be, as we work in an open plan newsroom with people working all around us, talking right behind us at times, and it manages to cope, so long as it's set up with the sort of environment that you will be working in. So if there is a bit of background noise when you work, make sure it's there when you're training the mic etc. We tried IBM as well but found it to be nowhere near as accurate. One problem is though that its settings can be a bit odd at times and difficult to navigate, and we all switched off the "commands" built into it, so that if it mishears something, at least it's not trying to open MS Outlook or something else, which it did with us for the first few days we used it.
My boss is very into it though, and certainly it's been a godsend for the live show we have to subtitle from 1am to 5.30am. Typing that live for that amount of time was killing!