I pretty much constantly keep my laptop plugged in at home since the battery life doesn't got much beyond what the Wii U Game Pad does. It's not an issue with that piece of hardware, but on the other hand I'm not using my computer like I would a motion-based controller.
The issue that's come to mind is having to move around the Game Pad as a viewfinder, scanner etc., and the attached wire could make that a bit awkward. Maybe you have just enough length on the cord, but one quick pull in the wrong direction and it becomes an annoyance.
As well, most Wii U households will only have 1 Game Pad per system for quite some time (perhaps years). Game developers are going to be designing game experiences around that. You and your family/friends may be playing a game where you have to pass the Game Pad to the next person in order to complete a puzzle, task, etc. Being tied down by a cable can make it a bit less convenient.
Of course not all Game Pad's are going to be plugged into the wall 100% of the time. But much of the time games will be started without the controller completely juiced. And many times it won't be long before it needs to be plugged in a gain, even after just an hour or two.
The low battery life isn't the worst thing in the world, but it's definitely something that I'm going to have to consider when I'm thinking about which next-gen console to purchase. I'll even get annoyed when my laptop battery dies, so that sentiment may very well be amplified if I'm in the middle of a killer multiplayer game with friends and the Game Pad goes. It's a bit disappointing, and certainly I'm on the fence.
