One idea that I've just thought of...
Because the PS3 will have a 60Gb HDD, you'll be able to store music etc. So, on GTA4 you would have your normal radio stations that Rockstar make but then you could have a couple of customizable radio stations (they start empty until you add custom music tracks) of about 10 tracks. You would be able to change tracks and have a least 5 customizable stations.