As Ted points out, demographic information is valuable both to podcasters and to potential advertisers. Any way you can collect that type of information from your audience is good.
I do see a few sticking points with Ted's idea, however.
- You're going to have to spend either time or money too create your transcripts
- I don't see a huge demand for podcast transcripts right now so I'm not sure how many respondents you would get
- The true power of a transcript, in my opinion, is that it makes your podcast searchable by search engines. In order to realize that value, however, you need to post the transcript on the web. If you post it...who's going to fill out a survey to get it?