iTunes radio has 20 million listeners

"Apple said its new streaming music service iTunes Radio has about 20 million listeners, the company revealed during today’s big media event in San Francisco.
The listener numbers have nearly doubled since the last time Apple shed some light on the streaming service’s usage just a week after launching back in September.
iTunes Radio functions quite a bit like Pandora, the leading streaming radio service in the U.S. You create smart radio stations based on a song or artist that’s already within your music library. For perspective, however, Pandora currently has 72.7 million listeners — and is actually able to generate revenue from the service from advertising."
Source:  VentureBeat, 22nd October 2013
Also - 1 billion songs played in just over 1 month
Note - It's only available in the US so far