Essentially, Twitter #Music is just a new chart system that ranks songs popularity based on data collected from the data in the twitter-verse. By default, users can listen to previews of songs on iTunes. There is also built-in functionality that lets users listen to songs with a premium account on Spotify or Rdio.
There are 5 types of charts that each user has access to. Here is what they are, along with their official descriptions on Twitter Music:
Popular - New music trending on Twitter
Emerging - Hidden talent found in the tweets
Suggested - Artists you might like
#NowPlaying - Tweeted by people you know
Me - Artists you follow
So there you have it. Is this the future of music? Is this just another doomed music discovery service in a marketspace that's already too crowded? Only time will tell.