I have all 3 of the main issues that I have heard Wii-U owners having problems with:
1. System freezes and make a buzzing sound. The only way to fix is to unplug from the back and reset.
2. Long loading times between apps and games.
3. "Rainbow" marks on the gamepad screen that can be seen when the unit is off and held at an angle or under light.
I contacted Nintendo Support and was asked to send in my console, the gamepad, and a game to check the freezing issue. I am definitely disappointed to now have to wait for up to two weeks to get my system back.
Two big concerns out of my call with their customer service:
1. The lady did not acknowledge that these are known issues, even though there is a note on the official forums about the loading and the freezing.
2. I am not supposed to use the original packaging to send back the Wii-U and they are only sending me a shipping label. The CSR said to just wrap everything in bubble wrap and send it back in a box. I was expecting a pre-molded box to be sent to me so I can safely send in my console. I am very concerned about how safe everything will be "wrapped in bubble wrap".
All in all this has been a major bummer. As I am typing this, my kids are playing Scribblenauts. Sure enough, I hear the loud buzzing and see the frozen screen... *sigh*.