Sony Music Unlimited is a subscription based streaming service from Sony like the Video Download service and the Playstation store.
You just need one account and you will be able to access all three services. Subscription will cost you 9.99 Euros a month (In Europe) and it gives you access to over 50 million tracks from all over the world.
The main advantage of this service is that it’s supported over a wide range of devices including the Sony Playstation, PS Vita, XPERIA smarthphones, Sony tablets and BRAVIA TVs and BluRay players (2011 onwards – with internet connectivity).
The web service supports both Windows and Mac OS. It also supports all Android phones and thus even non-Sony smartphones that are powered by Android can access this service.
All your playlists etc that you’ve created through one device are accessible through all other devices using the same account.