Mine has. I was playing Sonic & All-Stars Racing Transformed and I was racing in Samba Studios as Tails. On the final lap, I was making a left turn on the track and the game suddenly froze. The audio (music and the car's sound effects) were still playing. The video on the television screen AND the GamePad were both frozen. I had to do a hard reset on the system and the controller. Since that happened, I didn't pick up the system again (I got distracted by doing other house chores).

So has a game or the system itself actually froze/glitched on you while playing? I think it was just the game itself that did it for me.

So far, no.

It happened to me once when I was playing NSMBU. I'm sure Nintendo will fix it soon.

Yes

I've heard a lot of people mention freezes while playing. I hope it isn't a hardware problem; we really don't need another RROD fiasco...

My console froze once coming out of the internet.

Apparently there is a fix coming:
http://www.zeldainformer.com/news/comments/wii-u-freezing-hard-lock-patch-coming-next-week#When:15:00:44Z

"Either way, someone over on Reddit got confirmation from a Nintendo customer service rep that Nintendo is rolling out an update next week to fix the issue. Just to be sure our chain wasn’t being yanked, I too called Nintendo’s customer service and indeed got the same response. I also sent an email out to our PR rep for official word on the matter from a higher up, but so far no response at this time."

3 times.  None during actual gameplay though

it's happens to me on my ps3 from time to time as well. as long as it isn't too frequent it really isn't a big deal.

I think a very high number of people with WiiU's have had this hard lock. I've had it twice once in game and once just going through setup.

It'll obviously be fixed soon, just software related.