Spotify's free accounts are normally restricted to ten listening hours per month. If you really, truly love a particular song, you'll only be able to stream it five times in a given month. These caps will come on top of the usual limitations of free accounts: You have to listen to advertisements and there's no mobile access.
For $5 per month, users can eliminate the listening caps and advertisements. For $10 they can get access to Spotify's giant library of music from their smartphone. For many users, the mobile version of Spotify can serve as an iPod-killer, since it allows them to merge their own MP3 collection with the company's massive selection of albums in the cloud.
The question of whether users will convert to paying customers is crucial to the viability of Spotify's business model. The company has deals in place with all of the major music labels and many independent ones, but those relationships are not necessarily set in stone, nor did they come about easily. Its U.S. launch was delayed due to extended negotiations with the labels. More recently, concerns have been raised over the relatively small payout seen by artists, a few of which have opted to keep their new releases off of Spotify.