Kottke nails it
Tuesday, March 20, 2007 by Dave Winer.
This is why social networks for podcasts don't work, and why they do work for photos, blogs and twits (140-character SMS-style messages). 
Kottke: "With podcasts, you've got all that data locked up in binary format (no easy cut-and-paste) and it takes you 20 listening minutes before you can react to it (by commenting, by linking, etc.). With blogs, the reaction time to a post is 1-2 minutes, with Flickr it's 5 seconds, and Twitter is 2-3 seconds. The barrier to entry for reacting to and remixing podcasts is just so much higher."
