Gotta go fast!
Nintendo has uploaded a video to Youtube showcasing one instance of the improved load times scheduled to be included in the upcoming Wii U firmware update. The video shows a comparison video of a person closing a game of New Super Mario Bros. U and returning to the main menu. After the update, it seems to take the system 6 to 7 seconds to fully return to the main menu, which is about a third of the time it currently takes, which is about 21 to 22 seconds.
Watch the video below to see for yourself.