Nintendo has issued another system update for the Wii U. This latest update brings the firmware to version 3.0.1. Here's the official description:
Version 3.0.1 U
Released: May 20, 2013
Further improvements to overall system stability and software compatibility.
As you can see it simply improves stability and doesn't appear to add any new functionality. As always, don't unplug your Wii U during the update or you might end up with a bricked console. You can read the instructions for performing a System Update on Nintendo's official website via the link below:
How to Peform a System Update - Nintendo.com