We've been following this for a while and it happens today at 5pm pacific. Looks like the music store will have EMI, Universal (which just bought EMI), and Sony firmly on board with Warner being the sole hold out. I hate to be dubious (okay, maybe I like it a little bit) but it's hard to imagine this really rising to be a legit iTunes competitor. Apparently the service will offer some kind of sharing feature, presumably through Google+. Which is nice. Not sure it's enough to make Google+ into a major social competitor or Google's music store into a major iTunes competitor. But maybe it's enough to be a placeholder and serve some Android customers.