I can't say anything about the app as I've not used it. However, the concept is (in my opinion) flawed for a large number of potential users - the music my friends listen to is absolutely no indication of what I might like.

I'm too old. I've spent the past 30 or so years (I'm 36) developing a taste of my own. I no longer meet or socialise with people around music (eg go to gigs with friends). Similarly, my "favourites" are people I admire and respect for things entirely different to what their music tastes are. Most of the new music I find these days is based on what I listen to already or in curated theme-based playlists from sites like http://ShareMyPlaylists.com. Automating something like music discovery from a social graph is skewed (in my opinion again, and based on instinct rather than science) towards young people who still socialise in what I would call "taste networks" - groups based around shared tastes. Older people don't do that in my experience.

Good luck with it though. There's still a giant market out there. And I'll still try it just to see what it thinks I might enjoy.