Thanks to an alert reader, it appears that JustMusicStore is down (and iSOUND as well!). Whether this is temporary or not isn't known; but since they haven't been accepting payments lately, perhaps they are going to open up shop elsewhere - or maybe this is just a temporary thing.
I'll keep you posted!
Edit: JustMusicStore is back up, folks!
Based on a rating at the bottom of the JustMusicStore review, it appears that payments are down for this site as of June 24th, 2007.
If the status changes, this page will be updated.
EDIT: I suspect that they will have things running again soon, but I haven't heard anything to inidicate when. I'll keep you posted!