Ask any user of iTunes what he would change about the service, and his response will most likely focus on one thing: the inability to download music that he has purchased to more than one device.
And if he gets angry as he points that out, he is entitled to feel like that. The way everything stands right now, a person who has an iPhone, an iPad and an iPod is not allowed to download music that he has purchased to more than one of these devices.
Apple is well aware of that, and has begun negotiating a deal that (if successful) will enable users to have their music on all their devices. The key here would be either letting users stream their audio (a la Pandora or Grooveshark), or letting people download songs that they have purchased once unlimitedly.
The latter alternative is the one Apple is actively looking into, and negotiations with Universal Music, Sony Music Entertainment, Warner Music and EMI are underway.
If an agreement is effectively reached, it will be the start of a whole new stage for iTunes, and a decidedly hard blow to services like Pandora and Spotify.