Rdio lets you bounce around, trying new artists, in ways that have never been possible before. The artist you're listening to at that second also has a biography, a complete discography (often satisfyingly deep, especially in b-sides, live albums, and rarities collections), and a list of similar artists, artists that have been influenced by and were influences of whatever is playing at that second. You can jump from song to song, album to album, genre to genre, like you would on Wikipedia: follow the trail from The Who to Big Star to Matthew Sweet to Zumpano to the New Pornographers, and find out that the second rhythm guitarist in the New Pornographers has two great solo albums. Or use the recommendation service, or the Pandora-like "radio station." Or just look at what your friends are listening to--these services are all deeply intertwined with Facebook and Twitter, and it couldn't be easier to recommend or receive recommendations from people you actually know. For music fiends, it's like stepping through a door into a totally new world: suddenly, everything you've ever wanted to listen to is there, and you have the tools to find it.