Well Nintendo is urging you not to, at least not yet anyway. Wii users will be able to transfer all of their data to the new console including saved games and Wii shop titles as long as both consoles are hooked up and running at the same time.
In an official statement from Nintendo, here’s the details:
Wii U owners can wirelessly transfer content such as Miis, and WiiWare and Virtual Console games to their Wii U systems. Both systems will need to be connected to the Internet and the Wii U will need an SD card to facilitate the transfer. The process is very similar to transferring content from Nintendo DS to Nintendo 3DS or from Nintendo 3DS to Nintendo 3DS XL
This is amazing news for those players who were worried about leaving all of their precious data and gaming hard work behind with an upgrade. Say what you will about Nintendo, they really do seem to care about their fans.