Phil Windley attended a podcast show, and I picked this out from Leo Laporte (of TWiT):

Leo mentions that TWiT has started to take ads. Interestingly he gets quite a bit of pushback from listeners saying things like "now that you've started running ads, you'll never be honest about Dell again..." Certainly, this is no different than technology magazines or technology Web sites, but people feel differently about the editorial conflict of interest. Perhaps this is because podcasts are more intimate? He's not sure.

That's an interesting tidbit - I think it falls into the narrowcast model. When you have a magazine that's trying to appeal to a wide audience, the ties don't seem as close - but with the niche audience of a podcast, they seem to. I haven't paid much attention to the ads on TWiT, and I listen every week - great show, IMHO.