Nintendo Network accounts locked to one Wii U for now
Anyone setting up a Nintendo Network ID on their brand new Wii U will have their account locked to the Wii U they set the account up on, for now at least.
This means that, if players want to log in to their Nintendo Network account on a friend's console or if they need to replace their own console for some reason then they will not be able to access their original Nintendo Network account.
In addition to this, each machine is limited to having 12 different accounts activated from that system. This is fine for brand new machines but it limits how many accounts can be activated from the machine if it is sold second hand.
The Wii U support literature offers some hope for the future saying, "In the future, you will be able to use your Nintendo Network Account with future Nintendo consoles and other devices, such as PCs."