Nintendo has put out a Nintendo Direct video in Japan explaining the Wii U's storage system, and it is likely to make some people unhappy. While the video is in Japanese, the folks at Kotaku have explained it all.
It turns out that a big chunk of the internal storage that comes with the Wii U, either 8 GB for the Basic or 32 GB for the Deluxe, will not be available to users. First off, formatting the memory shrinks it in some way, so the Basic will actually have 7.2 GB and the Deluxe 29 GB.
On top of that, the Wii U keeps 4.2 GB for things like account data, leaving 3 GB or 25 GB of free space.
Nintendo has promised to sell all their games online, but if you've got a Basic , you won't be able to download too many games to your Wii U's internal flash memory; you could buy the 2 GB New Super Mario Bros. U, but the 3.2 GB Nintendo Land wouldn't fit.
Of course, the Wii U does support external storage, but there are some caveats. You can use an external USB hard drive up to 2 TB, but the drive will have to include an external power source. If it's a portable drive that pulls its power from USB, you will need a Y-cable, which connects the drive to two USB slots at once.
You can use flash USB memory, but Nintendo says doing so can impact gameplay.
This information follows up a previous report on NEOGaf, also translated from Japanese (Nintendo is giving a lot more information in Japan than in the U.S. even though the console is shipping here earlier) that games cannot be downloaded to an SD card.
It's enough to make your head spin.
This is the sort of thing that makes people doubt Nintendo's understanding of the online world. Nintendo has announced that they'll be selling all their games through the eShop, yet they're not offering enough storage, even in the Deluxe, for gamers to do what they do with the 360 and PS3; download a lot of games and have them all available. And using external storage seems needlessly complex.
It has also been reported that, while downloads are attached to an account, you cannot take your Wii U's external drive to a friend's house to play the game there, something you can do with the 360 (you just have to log into your Xbox Live account).
Of course, you can still buy games on disk, and you could download several small indie games to even the Basic Wii U, but this is a case where Nintendo's attempt to play catch up with its competitors falls short. Alas, the Nintendo mindset that once discouraged gamers from downloading a lot of games seems to still be prevalent.