for 9.99 you can listen to any song you want on your iphone
you can load up to 30,000 some songs FROM YOUR HARD DRIVE and have them available for streaming on your iphone
that means have access to all your music, in high quality streaming, with maybe 1GB of space taken up on your phone.
most new releases are advertised on spotify and the apps on the desktop client are decent as well.
I have tried MOG, Rdio, and Pandora, nothing touches spotify. 10 dollars is a steal and it surely will only increase in price as the labels become more demanding.
there are a few issues but overall its still a great service and whoever says its not worth the 10 is too cheap to have paid to use it