In anticipation of the iOS 5 announcement tomorrow:
You know who could use voice commands and speech to text in their iOS devices? Anyone that works with gloves on all day. That includes laboratory scientists and hospital staff.
I've heard a number of people suggest that iPads would work great in the lab for recording experiments. Not so. Any bench worker will tell you that removing your gloves every time you need to record a bit of data is a real deal breaker.
Now if Apple provides deeply integrated voice services, then a whole new world of use cases open up.