Social features are the primary thing I miss from rdio.com, but they have explicit "friending", otherwise you'd see nothing. I assume Google would use all their data to show you everything everyone is listening too and provide little control.

Google doesn't get social. I can't even share a photo from Google Photos onto Facebook that shows the actual photo; at best they'll share a link with a small thumbnail – at worst it prompts people to login to see it and shows nothing of value on FB. I get it...they're competitors...but the effort required to share an "Google Awesome" photo drives me away from sharing the good stuff they do do.