In reply to John Workman:
Yes, I have a reasonable amount of experience with it. My Dad also uses it a lot.
You will need a good quality microphone (iirc mine cost about £100). A headset mic will do fine, but it needs to be good. Also if there's background noise, it can stuff things up a bit. If you're at home, you shouldn't have a problem with that. But I've found it poor to use in open-plan offices.
It's good for general composing of text and basic commands. I wouldn't use it for excel, it's just not very good at moving between cells and you can't really do formula with it. It'll be great for emails, word and forums. Especially if the emails you can tolerate the odd typo, as it's not 100% perfect.
Put plenty of time into making sure that you teach it your voice. If you just do the bare minimum, then you'll be disappointed. Spend a decent while getting it setup just right and it's generally pretty decent.