Do you think Miis will be used as an account, xbox-style? So you can have your own Mii and your personal settings for it, as well as use it for an Online account?
I think that would only make sense. You could enter your Wii friend code and then the specific Mii account to add a friend online.
Well when you send letters to friends over the internet you can attach a Mii picture. So they pretty much are but youre not restricted to having my avatar all the time.