We are already aware that you'll need to update your Wii U fresh from the box to include key features such as Miiverse, Tvii, Wii U Chat and eShop.
However, another very important feature in this update is Wii functionality. As you will no doubt be aware, the Wii U will have backwards compatibility with Nintendo's previous console - but it's not ready out of the box. IGN has reported that upon inserting a Wii disc into the console, they were notified that an update is necessary to play the game.
This won't be a massive issue for many people, but there are still those who don't (or can't) connect their consoles to the internet. Right now it's already pretty clear that if you're one of those people then you are going to miss out on a vast majority of the Wii U has to offer.
Hopefully we'll hear more as to whether those without an internet connection can update somehow to play their Wii games - could Nintendo include important updates on retail game discs, for example? Let us know what your thoughts are on this topic by posting a comment.