Starting next month, you'll finally be able to share your Nintendo Network account across both the Wii U and 3DS. Nintendo just announced an upcoming system update, set to be released in December, which will let users sign into their Nintendo Network account on the 3DS using the same ID as the Wii U. This means that your eShop account balance (used for buying games and other digital content) can be shared across both devices, so that you don't have to worry about managing two different balances — a minor, but frustrating, annoyance for owners of both the Wii U and 3DS.
The update will also include another long-awaited update, as Nintendo will finally be bringing the MiiVerse social network to the 3DS. The service was previously only available on the Wii U and, more recently, on the web, and Nintendo had previously revealed that a 3DS version was in the works. You'll be able to check out both features when the software update rolls out for the 3DS next month.