A recent BusinessWeek article suggests that podcasting will grab more of the multibillion-dollar online advertising pie in the next five years.   The research firm eMarketer is soon to release a report that shows advertisers will spend more than $400 million on podcasting by 2011.  That is up from $80 million last year.

One factor motivating the growth is the expectation that Google will refine its podcasting services by developing the ability to insert audio ads, based on keywords, into audio podcasts.   In short, they will create some type of AdSense version for podcasting.

Another company making strives in opening podcasting up to advertisers is Podtrac which recently unveiled a free online service that enables advertisers to research audience information for audio and video podcasts based on demographics, size, and other characteristics.

Many mainstream media companies such as Clear Channel and CBS Radio are also moving to embrace the medium which many see as another positive in shifting podcasting more to the mainstream.  The ability to target a more specific market or niche definitely has its appeal for advertisers.