Google Labs might be dead but Google continues to use the labs branding for testing new functionality in their various services.
Google Music is the latest service to get a labs section.
1. Desktop Notifications: This one was much needed. Some browser extensions add this feature to Google Music. They are no longer needed. We still wish Google allows for music controls when the music app is not in focus!
2. HTML5 Audio: Google does not have to deal with DRM with Google Music as the music played is supposed to be owned by the user. As a result they can offer pure HTML5 audio playing experience. Adobe Flash Player is no longer required!
3. 5 Star Rating: Instead of thumbs up and down, you can select to rate songs on a one to five grade.