Pay attention folks -this is the next big thing. I use it like Tivo, so instead of TV on demand, I get music on demand. I subscribe to World Cafe, on WXPN, and also to a couple of other NPR shows, and download stuff from audible.com. I agree with David Winer's skepticism about making this commercially lucrative. It certainly can't be right now - it's still a fledgling medium, but even if it grows to the size of the blogosphere, I suspect that the audience base will still be so boutique and nuanced, that getting any kind of advertising revenues out of it are slim, otherwise, you might as well be in mainstream radio distribution.
Nonetheless, if you haven't tried Podcasting yet, get on board. It's a lot of fun. You can download the free software to get started here.
UPDATE: In a related article, the Wall Street Journal discusses blogs and advertising. The bottom line? Too early to tell......
