This story reminds me of a similar one I read in the days of Pandora's infancy.  According to this article, things haven't changed much since then, when musicians and music-minded people got about $10/hr. to sift through stacks and stacks of CDs, applying categories from the Music Genome to each song/artist/album, etc.

I want to think that things have changed so substantially in the past few years that Shazam can just automagically feed their beast every song that comes along.  Turns out, though, they still have to use a considerable amount of brute force:
Mr. Slomovitz, a music industry veteran, spends his days tracking down hot new artists — but not for a big record label. Instead, he works for Shazam, maker of the application of the same name that can figure out what song is playing in a bar, a clothing boutique or a TV commercial.

"It's like a scavenger hunt in real time," said Mr. Slomovitz, 42. "It never stops."

Mr. Slomovitz's job is one of the more unusual in the new digital music era, as he and the dozen or so other "music sourcers" at Shazam try to ensure that any songs the app's users might want to identify are ready and waiting in the company's database.
Of course, some of the higher-profile content comes to Shazam straight from the record labels, but consider:
"If we don't have a song that is being played in nightclubs because it is only on vinyl that isn't signed to a label, or was created on a computer," Mr. Fisher said, "hundreds of people could be tagging that song and getting a nil result." He declined to disclose the service's failure rate.
"If all the college radio stations are playing something new that's coming out of a school in Connecticut, that should be in there," he said.
I started reading this article thinking "OK, there's a lot of music out there, but this is a finite task like mapping all the roads in the US.  It'll take some effort, but it can be done."  But now I'm not so sure.  The music world is impossible to encompass.  The mapping analogy fails, because people aren't building new roads in their bedrooms or nightclubs every day.  And, worse, it's a great big world:
Because Shazam, which is based in London, is available in more than 200 countries, the company has a lot of ground to cover. "We have people in London, Japan, China, Indonesia," Mr. Jones said.