OK, so I'm a little annoyed at the current implementation of the memory card in the Wii. Sure, you can use it to view photos on the Wii and backup your save game data, but that's it. You can't access save game data on a SD card from within the game.
But I think the worst thing is that you can't access Virtual Console games if they're only on the memory card. You have to copy them to the internal memory to play them, which is where they were in the first place, and there's really no reason for you to back-up the data because Nintendo needs to "retrieve" it if your Wii breaks since it's tied to the console.
I think being able to store VC games on the SD card is probably the most needed feature, because it seems like VC games can end up taking a lot more space than save game data. I don't want to have to start manually swapping data between the card and the internal data to be able to play a game.