Nintendo has released a new 700MB system update for Wii U. Version 4.0.0 U offers the option to play Wii games off-screen using the GamePad. But, there's a huge caveat: you won't be able to use any of the GamePad's buttons on your Wii games. Even games that offer Classic Controller support are not exempt to this rule. I tried out Super Smash Bros. Brawl after installing the update and received a "Wii U GamePad controls cannot be used on Wii games" message when attempting to use the GamePad buttons.
Other features include the ability to automatically receive software and demos from Nintendo using SpotPass, support for USB keyboards, and a new friend list icon on the Wii U menu to make it easier to connect with friends.
The internet browser has also received a number of tweaks, including the ability to move forward and backward in a video using the L and R buttons, the ability to save username and passwords on sites, and support for viewing PDF files.
For a complete list of new features for update 4.0, visit Nintendo's support website.