I don't want to discourage your progress with DRM-free online music stores. They are interesting to me in a way that DRM-encumbered services are not. But while you only offer MP3 files, and not files using an open lossless format, it just doesn't work for me.
(Radiohead's experiment excluded. I can't explain why I am willing to pay 40 pounds for their new album in a nice box two months in advance of receiving it. But being able to download it while I wait for it to arrive is a bonus.)