Tim Westergren is one of those entrepreneurs who built an online company to fill a void he saw in the physical world.
His Oakland-based Pandora is the leading radio service on the Internet, which has to be satisfying for a musician who says he spent a "long time trying to make a living" in music beforehand.
In fact, Pandora, which recently filed for a $100 million IPO, now hosts a database of some 800,000 songs from more than 80,000 artists. This massive playlist is what you have to choose from in order to populate your own private music channel.
Around 80 million registered users have chosen to do just that, probably half of them via Pandora's iPhone app.