I've listened to a few podcasts before. And in my LiveJournal blog, I make a voicepost every few weeks (often I just read a poem or talk about something while walking down the street).
I think audio adds something very nice to the Internet. It's good to receive some of the parts of communication that are present in tone of voice and accent that are just not there in text only.
And here's the unusual thing about me and podcasts. When I'm actively involved in learning, I primarily receive information by listening. I listen closely, take few notes, and remember very well.
However, I find it difficult to listen to audio without seeing the person (this is equally true of audiobooks), unless I'm doing something else as well. So, I can listen very well while working out at the gym, while cooking, or while doing something else. But it's hard to focus on actually learning something this way.
But I still find the occasional podcast of value. I already had one or two set up in my Bloglines account, so I didn't add any more. I don't often listen to them--primarily because it's not possible to just glance over to see if I'm interested enough to pay close attention. Instead, it's necessary to actually listen!