Advertising Age has an article about Apple's plans to allow advertising within iTunes. According to the article: "Apple's current plans call for the ads to appear only in the lower-left
corner of the iTunes library while users listen to podcasts from their
computers rather than from portable devices."
Huh? In case you don't already know, podcast publishers can already control this by creating an "enhanced" podcast, which is very easy to do. How is this something new? Heck, even without creating an "enhanced" podcast, the artwork associated with your podcast shows up here.
The only "new" scenario would be if Apple allowed an advertiser to display an ad while someone else's podcast was playing... and I'm not sure that would go over well. Read the full Advertising Age article here.