I originally used the 2GB SD card that came with my 3DS since it had enough space for a fair amount of apps, games, and demos. However, in order to be able to download Donkey Kong Country Returns 3D (2.16 GB), I had to upgrade to an 8 GB SDHC card. I had it lying around, so why not use it? I plan on downloading Fire Emblem: Awakening too, so I will have a majority of the card filled. I don't see a need for higher capacity cards unless I decide to buy more digital games.