It's a few hours vs a few minutes.
No, believe me, it's not. I'm using the Google Music beta, and by my calculations, it will take multiple weeks to upload my collection.
http://www.wolframalpha.com/input/?i=80+GB%2F10KBps
I know I don't have the best internet connection, nor do I have the smallest music collection, but that's a whole lot of time to be uploading at full speed (which makes my internet unusable).