The process as it stands today is pretty straightforward. You download a helper app which finds and then uploads your music to your Google account of your choosing. Initial setup is pretty quick -- uploading music is, well, dependent on your connection, of course. Music syncs in the background, so you can go about your business while you wait for song after song after song after song to upload.
The Google Music Beta desktop app isn't actually a desktop app -- it runs in the browser.
More as we get it. For now, check out more screen shots after the break.