Some podcast stats for you, from Feedburner:
— FeedBurner points to nearly 6,000 podcasts now, up from about 500 in
— The average number of subscribers to FeedBurner-managed shows is up
to 33 from 15 last year.
— The top 20 most popular shows have "thousands of subscribers and our
couple of top podcasts have tens of thousands."
Addendum: if you have 5,000 subscribers, I figure that equals 500 listeners to a whole show if it’s really good, or 50 if it’s not. That’s based on my audiobook experience (as a writer, reader and listener).