I just went into my old Nintendo log in for the first time in ages.
Nintendo give you stars for registering stuff online which you can use to get Screen savers and sometimes games etc.
They've also started doing a recommend a friend thing, so if you want to sign up after getting a Wii I'll get bonus stars for it. (I think I get them for clicking too)
You'll want to do this as apparently it extends the warranty period Nintendo will cover it for.