Nintendo's new system features an 'automatic shutoff' feature, which turns off the system "if there has been no input for a set period of time," according to the system's manual. Here's the catch - a lack of input is still counted when a game is running and paused. We know - we had the system shut off on us when we left the system alone and came back after 90 minutes. System - off. Game progress - lost. By default, this option is activated, and appears to be set to activate after an hour, as we painfully learned.
All is not lost, however. This is able to be adjusted within the system options. You can turn the feature off entirely, or simply adjust the range of 'idle time' the system needs to register. All in all it's not a big deal - unless you don't know it exists. Then you might find yourself replaying a significant portion of a game, as we just did.