Notably missing, however, is Warner Music Group.
Despite that omission, however, Google Music, nee Music Beta, has a total of 13 million tracks, 8 million of which are live today, with the rest of them coming soon.
As before, with Music Beta, users can upload up to 20,000 of their own songs to their Google Music locker (no, there's no scan-and-match capability).
The store itself is part of the Android Market. Every song is a 320Kbps quality MP3, with a 90 second preview. Most of the music costs about $0.99.
But that all seems like every other music store around. How will Google Music differentiate itself from Amazon MP3 and iTunes?
For one, music purchased from Google Music can be shared with a user's Google+ contacts. Each of them can have one free play of a song, just enough to whet their appetites.
In addition, artists can open up their own "music stores," using the Google Music artist hub. As Google said:
"... any artist who has all the necessary rights can distribute his or her own music on our platform, and use the artist hub interface to build an artist page, upload original tracks, set prices and sell content directly to fans—essentially becoming the manager of their own far-reaching music store."
Google has also "arrange" for exclusive content from a number of big names, and much of it free, including content from The Rolling Stones, Coldplay, Busta Rhymes, Shakira, Pearl Jam, Dave Matthews Band and Tiësto.
Is it going to make much of a dent in iTunes' dominance? Honestly, no. But naturally this is all an adjunct to Android, much as music on iPhones via iTunes Match and iCloud is an adjunct to iOS; it's meant to be an attractant to people using Android devices.
The Android app, which is available for any device running Android 2.2 or later, will allow users to stream their collection to their devices as well as to "pin" music to the device, which allows a user to listen to it offline.
You can watch a Google Music video intro below.