I received my invite to Google Music a couple weeks ago. I've been using it in the browser since then. My Nexus S however, refuses to sync music.
Some people on the web report the same problem but it always fixes for them after awhile or after they do one of the following steps which have not worked for me. The settings menu simply does not appear in the Music App which would allow me the option to sync music.
I have tried the following things to no avail with exception of factory reset which I do not want to do.
The Sync Music option is not available in Accounts and Sync so the problem is not that this is not turned on as the option isn't even there.
I have uninstalled updates and re-downloaded the updates and that didn't help.
I have cleared application data and that didn't help.
I've probably tried other stuff too that I can't remember, and FYI, I'm using Google Apps so I don't know if this is a piece of the problem as well.