If I'm playing music in my car, I find the best medium is a flash drive. I can easily load a hundred mp3 albums on a flash drive. But I'm looking for cost-effective ways to mail music to people, and postage rates are getting higher and higher. SD cards seem like a perfect way to mail music. I figure the recipient can transfer the mp3 files to a computer or flash drive, and then they wouldn't have to fumble with a tiny SD card while they're playing music.