Wii U will be a Bring Your Own Storage party.
http://www.nintendoworldreport.com/news/30582
Wii U will support external hard disk via USB connection. At the Nintendo Analysts meeting at E3, Nintendo confirmed that the Wii U will not contain an internal hard disk, instead letting users provide their own storage using cheaper external USB drives.
While the Wii U will almost certainly provide a nominal amount of internal flash storage for game saves and some game downloads, the size of full Wii U retail downloads will require users to provide an external storage device of their own.
Nintendo confirmed that the Wii U will not contain an internal hard disk:(
Even on the current Wii, loading from the USB 2.0 ports is at least 3X faster than the Wii optical drive. I think USB 2.0 will be fine on Wii U as well.