I think it's great that there will be no audio ads. It will make it a much easier "sell" to on-board new users quickly. Whether it's crypto-currencies, messaging apps, social media platforms, many types of games or almost any type of peer-to-peer service the value is in the size of the network.
There has been a fair bit of discussion about the streaming services and I realize I'm still not sure exactly what is being offered. Most talk about streaming as a Pandora type radio service but will PeerTracks also offer a Spotify type service where I can tag the songs I like and have it stored for replay without having to let PeerTracks choose what I will listen to next?
Personally, as long as my music listening session isn't interrupted, I'm mostly ok with just about any kind of advertising. Perhaps artists or other companies can pay to be put on a rotation of ads that come as a modal pop-up upon signing into the PeerTracks site? Banner ads are an obvious option as well.
I think it would be also smart to build in some basic social features for free users with more advanced features for premium users. The idea being that free users can add friends or join circles or whatever to get them hooked, but then some of the more advanced convenience services would have to be unlocked by upgrading their accounts. I imagine it wouldn't be too hard to build in some way to message friends, post music finds on some kind of personal feed or wall you can share and also share custom playlists, possibly post them publicly and allow others to up/down vote them for people that don't want to build their own playlists and would rather search for some pre-built ones.
Speaking of social interactions on PeerTracks it might also be nice to build in some integrations other social platforms as well. For example, that way as a user I could link my PeerTracks account to my Facebook/Twitter/Google+ accounts and then with a button click share songs or playlists with my contacts on those services as well which would be a great way to have users inadvertently advertise PeerTracks to potentially a lot of people on already established social networks. Also maybe PeerTrack users could share with others more than just the songs such as info on bands or perks as a token holder of various artists as well.