There are more than one billion podcast subscriptions through iTunes

"Apple on Monday announced that the iTunes Store eclipsed 1 billion podcast subscriptions. That’s a whole lot of talking. A special promotion appeared in the iTunes Podcasts directory to commemorate the big number.
Apple says that those billion subscriptions are spread across 250,000 unique podcasts in more than 100 languages, and that more than 8 million episodes have been published in the iTunes Store to date."

Source:  MacWorld, 22nd July 2013