Steve Rubel of the great Blog Micro Pursuasion points to an eMarketer article that says:

The Podcasting report looks at a medium that has sprung up – with apologies to Steve Jobs – out of almost nowhere.

The audience for Podcasts has shown meteoric growth, particularly in the US. It is variously projected to reach between 20 million and 80 million by 2010.

While advertising on Podcasts is in its infancy, the nature of the audience and strong growth already have major brands investing in Podcast-based promotion. More advertising and sponsorship will inevitably follow.

I am asked all the time “What is the size of the Podcast universe?” Well, eMarketer is helping us to start to give relatively sane information to clients. I say relatively because – who really knows? My bet however is with eMarketer because we have yet to see the jet fuel that will come from smarter better produced shows as well as sponsorship dollars and Podcasts as stand alone marketing shows (Think of IBM’s current use of Podcasting.) This is all very much in its infancy and the best is still a ways out.