"Between December 2004 and 2005 the numbers of people going to the site grew from 6.1 million to 20.7 million," according to the report. "The figures mean that about 14 percent of the net's active population are regularly using the iTunes service."
"Consumers have clearly indicated that they are eager to control their own music libraries, one song at a time," said Jon Gibs, director of media analytics at Nielsen NetRatings.
In addition to looking at raw user numbers, Nielsen NetRatings also tried to find out who those users were.
The research revealed that teenagers aged between 12 and 17 years old made up a disproportionately large group of iTunes users, according to the report. They were more than twice as likely to visit the music store than any other population group.
The research firm also found that iTunes users comprise a readily identifiable audience in terms of their likes and dislikes for certain goods and services.
"For instance, Nielsen said, iTunes users were 2.2 times more likely to own a Volkswagen than the average internet user. Audi and Subaru were also popular with regular users of the Apple store."