Well i backed up my nand, transfered my wii data to the wii u. restored my nand, the only thing i can see is that you cant go back to the wii shop channel on the wii and redownload any purchased games to the wii. my wii didnt have any of my purchases still installed when i did the transfer, so i had to install in the wii menu thru the shop channel on wii u. but once you do that you cant re download them onto your original wii again. the process did go without a flaw as far as the transfer goes.
didnt check to see if the saved games and stuff were back on the wii or not after the restore of the nand. i'll update tommorrow and give you the results.