I think I've done this before. Well, not quite so much, I'm sure.
When I first heard about Google Music (Beta) I stopped at the site. I must've requested access as I got an invitation by email yesterday. I clicked through and picked three genres of music in which I was interested. Doing that provided approximately 80 free songs of a mixed and varied selection. They included tracks from artists such as: Usher, Elvis Presley, Al Green, TLC, and Whitney Houston. Next, I requested the new music app from the Android Market.
Today's step seems familiar as I uploaded 1.95GB of selected music to mSpot.com about a year ago. I noted today, that limit has been upgraded to 5GB. That's quite a lot of music as it can be converted to 64K bitrate for online storage. I do have quite an eclectic collection of music on my external media drive. So, I had to be quite careful and ended up uploading mostly 80's music to mSpot. I remember the process taking place over a number of days. I do sometimes stream music from this collection over my phone.
Google Music Beta is doing the same now. I just pointed the management software to the root music directory. It scanned for a minute and simply informed me that the process had begun for over 10,000 songs. It promised to continue the process until it's complete, even if I turn off my computer in the interim period. I'm doing it via my media computer which is always running. I guess it'll still take it a while ...
(My music is arranged into folders by eras. At the present time, Dean Martin is heading to the cloud.)