"Apple's integration of podcasting into its iTunes software has propelled the grassroots movement into the mainstream, but marketers say there are challenges to overcome before ad dollars begin pouring into podcasters' pockets. Among those challenges are finding ways of measuring listening and of efficiently buying ads on a medium that has so far been made up of small, fragmented audiences."
-- ClickZ
Earlier:
iPodvertising Possibilities
Podcasting: Advertising on iPod