I'm a pretty good public speaker. But I've avoided webcasting and podcasting because it's kind of daunting. In a smaller venue, the audience members are right there, and you can tell if you're not making sense. In a webcast, the feedback will be indirect. In a podcast it's seems like it would be nonexistent.
Also, I find that programming is an intensely literate experience. It's about reading and writing. A podcast -- listening and watching -- seems very un-programmerly to me. Perhaps I'm just being an old "get-off-my-lawn-you-kids" fart.
But I'll see how the webcast thing goes in January, and perhaps I'll try to do some podcasts.