iOS/Web: Most music discovery services rely on algorithms to deliver music you'll enjoy, but Piki, a new discovery app for the iPhone, aims to make finding great new music a little more personal. Tell the app which artists you like, and it will match you up and start playing music from other Piki users who like the same stuff.
Once installed, Piki asks you to start naming a few bands and songs that you already love. It'll add them to your profile as "picks", which serve as the base for the types of people you're matched up with (and who are matched up with you). Once you've added a few, the app starts playing songs from people who also like those tracks. From there, you can add more picks by name, browse popular artists to add them to your profile, add whole genres, and follow other users whose tastes match up with yours.
The app tries to get you to get your friends from Facebook, Twitter and other services involved, and to search for your friends on Piki already: since the service is new, they're likely not there, so the app pairs you up with a few of its most popular users instead. From there, the music starts flowing, and you can "repick" songs you hear that you like to better tailor the tracks the app chooses for you, send the user an emoticon-based note of praise for choosing a great song, or check out the song's tags to add them to your profile.
One nice bonus: the app supports background play, so when you leave it or lock your device, the music keeps flowing. Press power to unlock, and the album art shows on your lock screen.