I use e-junkie to sell Mac software and users are requesting a system like the App Store where all there purchases/downloads are managed so if they ever have an HD crash they feel secure in getting it back. Of course they can do this through me personally by contacting me and I'll send a download like but this system isn't as nice as Apple's.
Have you considered this before as part of e-junkie? If there was an API for e-junkie it's possible I could roll my own system for my specific customers but an e-junkie store sounds like a good idea imo.
Thanks.