SharkJumping offers six good reasons why the whole ads-in-podcasts thing is severly overhyped.
Reason #2: "Podcasting would appear to be subset of the Internet-connected PC business, meaning that you must have a device to connect to a PC to get a podcast. The closest analogue in the Internet -connected PC business is Internet radio since podcasting is essentially time and space-shifted Internet radio, which according to the Edison Research/Arbitron report Internet and Multimedia 12, has a monthly audience 8x as large as satellite radio, but which has an almost meaningless ad market associated with it, almost 10 years after the sector started. So, if it's at all related to Internet radio, or more likely, a subset of it, it's going to really small."