The bottom line is normal users (ie those who "don't know anything about this sort of technology") don't give a damn. It's a few hours vs a few minutes.
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).
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).