As usual, Scott Meyer gets it:
One very good reason to upgrade to Vista is if you’re interested in speech recognition. Vista comes with an extermely useful speech recognition engine built in. It’s still not 100% perfect, but once you spend a short time training the system, it’s good enough so that using speech recognition to write is now a valid option. There are still times when you need to fix the word selection, but you won’t be making typos or spelling errors.
So on the balance, if you’re a merely adequate typist (like I am), modern speech recognition tools can significantly reduce the time and effort needed to write.