Although still highly “niche,” the popularity of podcasting has grown by 18% year over year according to Edison Media Research (via Podcasting News). In their survey in 2007, 13% had listened to a podcast, up from 11% in 2006. (The 18% is lift: (13-11)/11=0.181818.) Awareness of podcasts has grown even more, from 22% having heard of the medium in 2006 to 37% in 2007. (68% lift.)
Video casting has grown from 10 to 11%, which is 10% lift. There is some doubt to whether this is accurate, since such popular vidcasts as Ask a Ninja and Rocketboom wouldn’t fit into the same definition as a podcast (ie they’re usually not downloaded for later listening or viewing).
Edison VP Tom Webster says of podcasting’s growth: