PodBlaze offers a white paper on the business impact of podcasting. It was airplane reading for me recently and it does have a number of interesting nuggets, as well as some data on forecasted growth. At times it is a little awkward to read and it veers between a business and a technical perspective — it actually includes a complete RSS example, for instance.
Overall, though, it’s worth a download and reading.
(Thanks to Steve Rubel for pointing this paper out.)