Imagine your music service of choice is Rhapsody and mine is iTunes. Or your use iLike and I use Last.fm. You use Spotify and I use Imeem. Or you use Blockbuster and I use Netflix. I should be able to follow your tastes, history and recommendations without having to join your service (or vice versa). We are now starting to see some lifestreaming apps/aggregators that solve the first piece of that puzzle.... I can see what you what media you are consuming without having to join your service.
But, currently when I see that you've played a song that I want to check out, the link takes me to your service provider, not mine. Sure, this is in your service provider's best interest (page view, conversion opportunity, etc.) but certainly not in mine. Now, I have to copy the info, got back to my service provider, and manually re-enter to find and acquire.
The way it should be (IMHO), is that the consumer of the media should get to decide what service provider fulfills it. Basically, it's a massive translation layer that can take content in from anywhere and map it back out to anywhere else.
This is what often referred to as the "resolver" problem. Back in 2007, there was a thread between Lucas Gonze, myself and a couple of other people where we talked about this issue... and who should take the lead in solving it.
In the absence of these "portable music identifiers", people that are passionate about greasing the wheels of taste and content sharing are forced to the lowest common denominator... MP3 search engines. This has been the basis of the projects I've been done recently.... mapping multiple services play history down to free-range MP3s (or at least what it could find). Of course, the rights-holders are not big fans of this approach (see "world vs. seeqpod" suits) - and the consumers are often frustrated by bad files, dead links and just poor overall quality of content delivery.
I've recently been vocal about the idea that the solution to this problem is an API platform that any/all services could use in lieu of MP3 search. Conceptually, an advertising/commerce supported (ok, subsidized in the near term) free-streaming catalog provider that most music could be mapped to - a fully licensed central digital music catalog(more on this later). Granted, this is a rather grandiose idea and anything in this industry that upsets the status quo is often met with resistance (at best) and endless lawsuits (at worst).
So, my rambling has finally led me to my point... content resolution. If there is no central catalog that everything can be mapped to, then what we need is that translation layer that lets content links be mapped back and forth across endless catalogs. Grandiose? A bit, but seems accomplishable without buy-in from the existing establishment. In fact, there is the very early stages of an open source project called Playdar whose goal is to provide the framework that lets content be mapped from one source to another - from the web to your local library, to your other networked devices, to your friends' machines, to music service providers, to search engines.
I'm pretty excited by the idea - I think it could enable some very compelling consumer experiences that the community is empowered to enable on their own.