Chad Dickerson notes a Forrester Research study on podcasting (Forrester Numbers on Podcasting). The report only briefly mentions podcasting but claims that in 2005 there will be 300,000 US households using podcasts, rising to 12.3 million US households by 2010. I take these numbers with a grain of salt. There will be many factors that will have a significant effect on adoption. After all, MP3 blogs have been around for quite a while, yet never really took off. There were several relatively minor technological developments that have spurred podcasting, and I think we can look forward to more relatively minor changes that will boost podcasting (or potentially inhibit it). For example, if they figure out a way to deliver podcasts to the car stereo, I think we will see many, many more podcast users. On the other hand, TiVo is simply amazing, yet penetration is lower than many have expected.

UPDATE 0940PT

I should have had this in my original post, but one should note that one way podcasting will take off is when Apple provides native podcasting support for the eponymous iPod, which has been announced by Steve Jobs, according to Dan Gillmor (Apple's iTunes to Carry Podcasts).