I purchased an SD card with my Wii yesterday, with the sole intention of storing all donwloaded VC games, channels and save states on the card.
However, I've found that even after the SD Card Wii update, I can only copy things to the SD card from my Wii. After trawling through the setup menus, I've not found a single option to specify where to save games, and where to download VC games to, so I've come to the conclusion that this feature has either been intentionally left out, or is still to be updated....
I even tried copying VC games to the SD card, and then deleting them on the Wii - the channels just disappeared until I moved the VC games back onto the Wii.
So I guess my point is... although I can see that an SD card could be handy for backing up save games etc, why were so many stores keen to bundle one in? It's not a particularly essential accessory with the current state of play.