An interesting study by Bridge Ratings indicates that the number of people who downloaded a Podcast has risen from 820,000 in 2004 to 4.8 million people in 2005. Projections of audience growth by 2010 is expected to reach 45 million users. More optimistic estimates approach the 70 million mark.

In my opinion the viability of podcast business models is still a few years away from being sustainable based on figures like this. I look forward to being proved wrong!