We got a tip this morning for the official URL for Google Music, and we've been randomly checking it (read: mashing F5 constantly) since then. A few minutes ago, something amazing happened - it went live. Hit the link, request your invite, and
patiently wait for it! GO!
After clicking on "Request invitation"
Although this just went up, we can pull out a few obvious facts right off the bat:
Honeycomb and Gingerbread will be supported
At least based on what's shown in the images above, Music doesn't appear to be a store.