Back in 2007 emarketer estimated that the total podcasting audience reached 18.5 million. That same report projected that by 2012 that audience would grow to 65 million in 2012 with 25 million of those listening once a week.
With more and more people sharing their stats it should be interesting. I'm hoping companies like Libsyn.com, Blubrry.com, and other networks will release their numbers at the end of the year. While most of the early projections in 2007 didn't focus on downloads, it should also be interesting to see those types of numbers. In 2008 Wizzard/Libsyn.com reported 1.2 billion download requests. In 2009 Libsyn.com (via Wizzard Media) stated a total of 350,053,574 downloads in quarter two (showing 45% growth over the previous year). Also back in 2007 stitcher.com didn't play much of a role (they had a beta in 2008), but they are increasingly becoming more and more popular and taking podcasting into areas where it had not gone before.
Also back in 2007 everyone was tied to iTunes. We synchronized our iPods or iPhones and if you listened to all the podcasts on your device, you had to go back to your home to resync your device. Now many have cut the chord to iTunes and are consuming podcasts on their smartphone.
As we near the end of 2012, I look forward to the numbers that are published. If you haven't started your podcast, now is a great time to start.