That button works now!
If you've been poking at that little Wii U icon on your GamePad since launch hoping it would hurry Nintendo and Hulu along, know that it worked! Hulu Plus is now live on your Wii U.
It's pretty neat how the GamePad works as a second screen and controller for the service. Or, use it as a portable TV around your home. A tour video on Hulu's page gives you a good overview of how it all works.
If you're not yet a Hulu Plus subscriber, Hulu is offering a 1-week trial to let you try it out on the Wii U.