Yeah, wii is a generic word and has been around for centuries. Go ahead and use it, but why stop there? register some more, they can not legally touch you...
Ugh, the above was sarcasm, it amazes the thought process of some "domainers" around here. This is the legal section, how about some legal point of view? It is a TM, hence there can be issues. As far as not ever being contacted about TM names you own, consider yourself lucky instead of being legally able to hold them.
Good test here, if you register something because you heard of a name, product or service, you are more than likely infringing on the name.