I tried to download the update to the Check Mii Out channel, and got an error while it was downloading.
No really big deal, except I was rather disappointed with the way the UI handled it. The download UI shows Mario from the original NES Super Mario Bros. running along the screen, gathering up coins that represent ... well, who knows what they represent. Chunks of data, I guess.
In any case, when an error occurs, instead of having Mario die (I'd suggest by Lakitu or a Goomba), they just display an error dialog and suggest trying again later.