Got my invite this morning to music beta. got about 15 percent of my library (7,000 tunes) downloaded so far. You just point the music loader at your music folder or iTunes and it uploads the whole thing.
I've got it streaming to my ipod touch right now through a browser. Kind of cool.
I was wondering about the invites too..I applied for an invite the very day it came out, and since then have been WAITING...and waiting..and waiting. Finally, a few days ago I received the long-awaited invite. Google Music is awesome! Its everything you need in a music app..hope y'all get an invite too! I know you'll love it.