The nuts and bolts of this process are fairly straightforward: After registering for a free Pandora account, the user creates a radio station by naming a band or a performer--say, the Yeah Yeah Yeahs. Within seconds, a Yeah Yeah Yeahs song will play, followed by bands that meet the Pandora search's criteria for Yeah Yeah Yeahs-esque sonority (in this case, "punk influences and electric-guitar riffs"), with the occasional Yeah Yeah Yeahs track mixed in. Each station you create is saved to your account. If you come back to your account later, each station will contain a whole new selection of songs--most likely by some of the same artists but in a different order. Of course, there is a small price to pay for the service, though it doesn't directly affect your wallet. Graphical ads are pushed throughout your listening interface, though you can always minimize your window to avoid them (more on that later). Another option is to pay for Pandora's ad-free premium service, which costs $12 for three months or $36 per year.
This is an imperfect system, since it's hard--if not impossible--to build a perfect set of "sounds like" algorithms. For instance, creating a station for Gillian Welch will render a plethora of the expected folk/country-tinged singer-songwriter ballads, but annoyingly, almost all of them will be by women. Presumably, a listener who likes Gillian Welch would also like, say, Will Oldham, Bob Dylan, Vic Chestnut, and so on--you get the point. A Pavement station unearths some bands with approaches so far removed from Pavement's detached delivery that it's kind of funny when they show up (New Order?). The success rate is fairly high, however--we did discover several decent new bands and artists, and occasionally, Pandora nails it: A Ghostface Killah station unearthed not just any old hip-hop tracks but a majority of hip-hop from rap's underground/indie artists, since Ghostface rests fairly far outside the mainstream top 40.