Actually, I think podcasts are more frequently like radio shows, but in a saved format. Many of the ones I listen to ARE originally aired as radio broadcasts (Dave Ramsey, Planet Money, Marketplace). I personally probably wouldn't be all that interested in just listening to someone read their blog posts, especially if it is something I read already. But good discussion and interviews that supplement the blog would be nice.
Actually, JD Roth of Get Rich Slowly and Jim somebody of another blog were doing a podcast about a year ago. It was kind of painful to listen to most of the time, but I stuck with them because I really like JD's blog. They ended it without comment, but anyone interested in this idea would be wise to talk with them about their experience. I am not sure how you marketize something like this. I think you would need to have a pretty good and professional "on air" presence in order to build numbers.
That being said, I would LOVE a podcast that had interviews with people who were ER-ed or SER-ed talking about how they got there and how they stay there, along with tips from relevant professionals. Kind of like this forum, but in audio version. Or Dave Ramsey without the political/social commentary. Again, whether or not it is something that can be monetized is a question. I wouldn't pay for it. I'm too cheap.