I have around 60GB of FLACs on my hard drive. At LAME's V0 encoding, that's around 20GB of MP3s. And it's ever increasing. Considering that SDHC has a max of 32GB and SDXC doesn't have much support (much less microSDXC), there's definitely a market for something like this. (Probably very niche, but eh... Amazon seems to be positioning this as kind of a Box.net thing with an emphasis on music storage and playback)