I use Dragon (Version 13, Premium) and find it a complete godsend. You do need a powerful enough computer, as other posters have said, but the specs aren't particularly high because my 2-year-old laptop doesn't have any problems.
It's also of limited use if you're working on a fiddly text where you have lots of tags or need to look up lots of terminology, but if it's something straighforward it transforms my normal typing speed of about 75 wpm into a speaking speed of about 120 wpm (or even more), with a consequent massive increase in how fast I translate the first draft! You do need to proofread carefully, though, because homonyms don't get picked up by a spell check...
I also found that Dragon needed very little training to be really amazingly accurate. I'd used other speech recognition tools in the past and found them almost useless, but this one is definitely worth the money. Although I gather that it's not available for all languages, which means that once again I'm thankful to be an English native speaker!
