maintenance yesterday. As detailed in last month's Nintendo Direct, the update also lets users tie a Nintendo Network ID to their 3DS systems, meaning they can register their handhelds under the same IDs used on their Wii Us. In turn, that means users can combine 3DS eShop balances with Wii U ones.
Once the update's completed, you'll find the green Miiverse icon in the top toolbar of the 3DS menu. You won't be able to access Miiverse without a Nintendo Network ID, so you'll have to create one for the 3DS, or register an already created ID, such as one your Wii U is tied to. After that, it's Miiverse city: You'll be able to post, scribble, attach screenshots, and browse to your heart's content. One contentment your heart has to wait for is Friends functionality, which isn't available on 3DS Miiverse at the mo.
We hoped to check out how the update affected the 3DS eShop, but at the time of writing we couldn't access it. According to last month's Direct, the update lets users purchase Wii U content on the 3DS eShop (but not play it on the 3DS!), and vice versa.