Nintendo is set to carry out extended maintenance on its online services today, ahead of the expected release of a significant Wii U system update.

As Nintendo detailed last week, the Wii U update will reduce system loading times and enable users to switch data between two USB drives.
The patch will be followed by the launch of the Wii U Virtual Console, which will go live in the US tomorrow, according to a Nintendo of America Facebook post, which suggests that the system update will be released imminently.

Nintendo UK's network maintenance information page says:

Extended maintenance:

From (approx.) Monday, 22 April 2013 21:00 to Tuesday, 23 April 2013 03:00 [1pm-7pm Pacific Time]

Affected Services:

Wii U - Nintendo eShop
Nintendo 3DS - Nintendo eShop
Wii - Wii Shopping Channel
Nintendo DS - Nintendo DSi Shop
During the extended maintenance, parts of the affected services may be intermittently unavailable.

Posted: Apr 22, 2013 10:51 am
Related Forum: Gaming Discussion

Source: http://www.computerandvideogames.com/402317/wii-u-extended-online-maintenance-planned-today/