in the late 90s i used to demo dragon dictate vs. ibm voice type? anyway dragon dictate would be used in siri, so thats good stuff. the most important takeaway is to have a great mic/headset. i'd use a plantronics headset w/ dragon dictate and then switch to a $1 toy headset w/ the ibm voice software. i don't know the software now, but i'm sure having the best mic you can buy will still net you the best results.
and yea this software was sold to lawyers and doctors, etc (different versions for obviously different vocab), there was also the basic general public use one.