Nintendo has scheduled some maintenance for the Wii U and 3DS eShop this Monday.
According to Nintendo, the maintenance window is from 1pm to 7pm PT on Monday May 30, during which time all network services will be affected. This means that services could be disrupted during that window, so it might be best to stay out of the eShop during this window if you can.
Additionally, Flipnote Studio 3D will be undergoing its own maintenance two days later. On next Wednesday June 1, between 6pm and 8pm, all network services will be unavailable for this title.
Let us know in the comments section if this downtime will affect you, or your own speculations about what the maintenance might be for.