This international survey has a lot of information on podcasting. The survey size is a little small, so the numbers are skewed a bit... but it is still a good read. You can download some of the statistics at: http://podcastersurvey.com/ipcs07.pdf. Some of the interesting findings include:
- Podfading seems to be a minor problem at the moment
- The European podosphere is commercially less ambitious
- Podcasting is not only attracting "techies"
- Podcasting is about identity and relationship management
- Most are interested in sharing information and expressing of opinions