As I've mentioned, independent musicians can fall prey to a lot of questionable business deals that promise to make them rich.
But Pump Audio seems like good way for independent musicians to earn some money. (Full disclosure: Pump is based in Seattle, and I'm acquainted with one of their employees through mutual music connections.) If you own the rights to your compositions and recordings--as the vast majority of independent and unsigned musicians do--you can license them on a non-exclusive basis to Pump. Then, Pump retitles and sublicenses these pieces to other content creators who are looking for a particular type of music--say, an instrumental surf piece for use in a TV spot, or scary music for a scene in a TV show.
Reading through their detailed FAQ, I don't see any major catches for musicians: there appear to be no up-front costs, you retain the full rights to your music, and if you later want to sign a record deal and the label refuses to allow you to sublicense your music in this way, you can write Pump a letter and they claim they'll remove your music from their database. The one catch, and it could be a deal-breaker for some artists, is that you have no control over where Pump places your music. It could end up in a commercial for some product or organization you despise. (Welcome to the world of licensing--it works the same way with some label deals as well.)
Today, Getty Images announced their intent to purchase Pump Audio. Founded in 1995 and also based in Seattle, Getty basically does with digital images (particularly photographs) what Pump has been doing with music, only on a much larger scale--the company is responsible for delivering more than 3 billion thumbnail images per month, garnered more than $800 million in revenue in 2006, and has offices in 21 cities. You see Getty-licensed images all over the place, in news stories, commercials, and stock images on Web sites. (Their main competitor is Corbis, which is owned by Bill Gates; a number of "microstock" sites, which license images from mostly amateur photographers at very low prices, are also in the market.)
Getty's huge customer base means more licensing deals for Pump, and more money for the musicians who license their songs to Pump. It's also a wise move for Getty--some music industry watchers predict that publishers will thrive the most as the current music industry business models--like CD sales--collapse.