Podcasting has something like 17% market penetrarion

According to data compiled by Pew Research for its annual State of the Media report, awareness of podcasts grew significantly last year. One-third of all Americans now say they have listened to a podcast; 17% said they had listened to one in the last month alone, as of January.

You know, over whatever the survey base is (US), but Pew is pretty legit.

Podcasting has something like 17% market penetrarion