Update (12/28/13 @ 4:02 PM): It looks like there are still some issues, and they are planning more maintenance.
@NintendoAmerica: We’re making progress, but to manage global traffic, we temporarily closed the eShop on 3DS. The outage will last until 4 a.m. ET on 12/29.
Over the holiday season. It seems Nintendo experienced much higher traffic volumes, and it has done a number on their servers, especially the eShop. Perhaps you have experienced some of these issues yourself. Nintendo has apologized both on Twitter and Facebook. Now, they have scheduled a maintenance time tonight from 4:00 PM until 4:00 AM, in an effort to fix the problem.
We sincerely apologize for the connection problems in the Nintendo eShop. We understand this is taking longer than expected, but we can assure you that providing a solution is our top priority. We are determined to make sure everyone can enjoy all that Wii U and Nintendo 3DS have to offer. In an effort to manage the high volume of traffic and ultimately improve your experience, we are temporarily taking the Nintendo eShop services offline between the hours of 4 p.m. – 4 a.m. ET. Thank you so much for your continued patience. We will keep you updated.