University of Cambridge psychologist Simon Baron-Cohen (yes, they’re related) and his research team have created instruments to measure two aspects of personality: the systemization quotient, which measures how oriented you are towards systems (anything with predictable inputs and outputs) and the empathic quotient, which measures how oriented you are towards people. People who are autistic tend to have very low EQs, but frequently have very high SQs. (You can measure your own SQ and EQ here.)
Pandora is clearly all about the systemization, with no empathic component – it’s practically autistic. Your friend saying “Best fuckin’ album I’ve heard in months” and sending you a link is all EQ, no SQ (and for most of us, that’s the killer app).
Baron-Cohen describes people who have similar EQs and SQs – that is, they are equally oriented towards people and systems – as being ‘balanced.’ Last.fm‘s social sharing and Hype Machine‘s ‘another user tried searching for [this band] next’ have moderate EQs and SQs. And The Echo Nest‘s Recommend + Analyze combo explicitly aims to have both a high SQ and high EQ – what people are saying about the music, coupled with its intrinsic characteristics.
Of course, just as with people, it’s all about the diversity of approaches.