Nintendo has made an update available for all you Wii U owners out there that adds "system stability improvements and other adjustments to enhance the user's experience".
Jargon aside, basically, all I've found it to fix is some occasional freezing after quitting some games -- specifically Runner 2, which froze every time I quit.
This 30MB update is a small taste of the larger update coming later in April, which really will fix UI load times. I can't wait for that one personally, because sometimes my menus will take 10-20 seconds to load per transition, which can get pretty annoying.
Wii U system update [Eurogamer]