I have just started using Spotify, which took me some convincing - I feared it would be yet another internet app a la Facebook that would suck precious time out of my life and prevent me from spending quality time with my wife and son (yes - the internet is responsible for most family-related ills. How do you feel now, Mr Tim Berners-Lee???).
But - it is quite remarkable. You can listen to pretty much any song you like. It's a veritable candy store of limitless musical treats (and I don't have to pay anything OR break the law - shiny!).
The good thing about it is that I can listen to stuff before committing to paying for a CD or download. I can also discover new bands just by browsing (or even typing in random names for fun - ever heard of Peter and the Test Tube Babies??). Not only that, but it's the perfect opportunity to indulge those guilty pleasures without actually having to buy anything (cough cough! Girls Aloud cough cough!).
The downside is, of course, that you can't take music away with you for your iPod or to play in the car. But it is free - and I don't actually listen to stuff much that way these days anyway.
The other major downside is the fact that there are millions of tracks on Spotify - I don't know where to start. There is such a thing as TOO MUCH CHOICE!