Customers may not understand that subscription services, like that offered by Napster, only give them access to their music for as long as they subscribe, according to critics.

While Microsoft's Janus software – used by Napster – lets customers download all the music they want and then wipe out their playlists and download more, they can only listen to that music as long as they subscribe to the service, writes NewsFactor.

Yankee Group's Mike Goodman suggests that this is an improvement on previous subscription services, which only allowed subscribers to listen to the music on the computer, but he adds that services like that offered by the iTunes Music Store – where music can be bought for 79p a track – mean "you essentially own it and can copy it."

The report states that subscription customers cannot copy the music to another device or burn CDs from their playlists.

NewsFactor concludes that: "The a la carte model pioneered by iTunes grants a perpetual license to users. That gives them leeway to move their music around and copy it to other digital media. And since the majority of hard-drive-based MP3 players sold have been iPods, a majority of downloadable music customers already are accustomed to that flexibility."