The number of music enthusiasts using iTunes, Amazon.com (AMZN), and other digital music stores has leveled off at about 40 million people, market researcher NPD Group reports. Audiences increasingly are turning to ad-supported streaming sites such as Pandora. While growth in downloads may pick up this year, Pricewaterhouse-Coopers says, it won't be enough to keep the overall industry from shrinking. U.S. sales of all kinds of recorded music—CDs, downloads, and other formats—will fall to $7 billion in 2012, or a bit more than half their level in 2005, before climbing slowly, according to PWC. "The days when people were building their digital collections or might hear a song and buy digitally are diminishing," says Russ Crupnick, an analyst at NPD.