If you got your hands on a Wii U and have yet to start its huge day-one system update, heed this tip from your friends at GamesRadar: Once you begin the update, DON'T TURN IT OFF! We love you, and we don't want your expensive new hardware to become a shiny plastic door stop.
Several users have reported their consoles were rendered inoperable after power interruptions during the 5 gigabyte install which can take several hours to complete, according to Ars Technica. Some have even tried to reset the console, thinking it froze mid-installation. Consoles tend to warn users off from that kind of behavior, but it's tough to blame people getting worried after an hour of minimal progress.
Of course, the patch is important--it adds functionality for Miiverse, the eShop, and some backwards compatibility. Just give it time, and maybe hold off if any huge winter storms are about to sweep through the area. Be careful about losing internet connectivity, too.
Fortunately, Nintendo's 12-month warranty should cover those with bricked consoles as a result of the update.