Techcrunch reported that Pandora is currently the fourth most popular free app on iTunes (behind Apple’s Remote, AIM, and WeatherBug), and has reportedly been seeing a new listener every 2 seconds. Usage over the weekend hit an all-time high for the service, with 3.3 million tracks streamed to iPhone listeners alone. Perhaps more impressive is the retention rate of listeners, who are averaging over an hour of listening per day.

The Pandora music stream is great on the new iPhones with the 3G and Edge networks.  Between the iPhone and Sonos Digital Music System, music lovers are no longer tied to their computer to enjoy the benefits of Pandora’s personalized music recommendation service.  Rock on.