Now that the Wii U is out in the US, more specific technical details are starting to come in. One thing Nintendo kept particularly quiet about, only releasing a few general details towards the end of the build-up to launch, was the Nintendo Network Account system. We learned the distinction between a Nintendo Network Account and a user account, that the former is used for purchases and friends, and the latter is used for saves, but that seemed to raise even more questions.
Finally, through the experiences of early buyers and the Wii U support on Nintendo's website, we're getting some answers, and they don't look good. Specifically, Nintendo says you can't log into your Nintendo Network Account on another console:
A Nintendo Network Account can only be used on the console where it was created. In the future, you will be able to use your Nintendo Network Account with future Nintendo consoles and other devices, such as PC's.
So, looks like your NNA is quite different to your Xbox Live account. And what does Nintendo mean by “future Nintendo consoles”? Does that include other Wii Us you might purchase in future, either as replacements or so multiple members of your family can play at once? It doesn't look that way:
Once an NNA has been created, it can be deleted from the system. However it cannot usually be transferred to a different Wii U.
With the word “usually”, Nintendo is being even more confusing. No clarification is given on the website, but I'm guessing NNAs can be somehow recovered in special circumstances, e.g. if your console breaks or has been stolen, by some process that requires confirming your identity. But if we can't retrieve our purchases and friends lists even in those cases, this is going to be a big problem.