I'm very interested right now in the possibilities of speech on pervasive devices, in particular apps running Windows Mobile. I looked into it and was helped by some useful posts from Mike Hall. It is still quite early in its development but a 3 year old demo app from Nuance which worked really quite well on my Pocket PC.
The problem is they don't have an SDK so you can't embed it into your Windows Mobile app or even see samples to see how easy it is to do. I really hope they change that - it only hinders people using their product.
I'll put updates here as i learn more.