To call something the most popular podcast might seem a little like identifying the tallest leprechaun, but the numbers are impressive for any media platform. “Serial” has been downloaded or streamed on iTunes more than five million times — at a cost of nothing — and averages over 1.5 million listeners an episode. That is as many people as watch an episode of “Louie,” the buzzed-about comedy on FX. Ira Glass, the host of “This American Life,” told me his show took four years to reach one million listeners. “Serial” raced past that in a month.
via ‘Serial,’ Podcasting’s First Breakout Hit, Sets Stage for More – NYTimes.com.