I set my Wii U to downloading and went to eat, so I don't know how long it took.  I haven't had any issues.  I checked out a website, transferred my Mii from my 3DS, played a very little bit of NSMBWU, and bought and downloaded Trine 2.  I assume that went fine, because I set it to turn off when it was done downloading, and everything was shut down after I watched The Walking Dead.  I guess I should check that, but so far, so good.  
To the person above complaining about the screen being cut off on non-HDTVs, it happens on my old CRT 16x9 set.  Find out if you can adjust the overscan.  I used to know how to do it and will have to figure out how again. Then again, I'm temporarily using component video until I can get an HDMI switcher (old TV, one HDMI input), so I may wait and see if my HDMI input is more correct.  As it is, Mario looked much better on the Gamepad than my TV.
While I'm at it, I was under the mistaken impression that those 3DS/Wii U eShop cards went into a pool and could be used for either system.  Nope.  Only works on the systems on which you redeem it.  Sucks.
I was able to confirm that Trine 2 downloaded.  That's super swell. I do wonder why it and New Super render on both the TV and the pad.  I wonder if you can tell it just to render on one or the other.