According to Mark McCrey, founder and CEO of Podtrac.com, Ask A Ninja is the top podcast and has over 250 million unique viewers that download its content as it becomes available each week. Then there's a YouTube audience and other delivery not tracked by Podtrac.com. That's quite a brand, anyone brave enough to send him the question, "How does a ninja feel about taking preroll advertising?"
UPDATE Maybe because I was sitting in the nosebleed seats at the ARF conference yesterday, or possibly because the panel occurred right after lunch when I was given a plate of vegetables at lunch (everyone else had beef) and was a little dizzy from the lack of protein, but the 250 million figure is apparently overstated. According to a release Podtrack posted about Mark McCrey speaking at the conference, Ask A Ninja is the video "most watched on a portable device" though it also said that 82 percent of its viewers watch online. It's still a significant audience.