According to a a new report from eMarketer, podcast advertising is expected to climb from $80M to $400M by 2011. What's interesting here is that experts predict that new Adsense-like algorithms that facilitate smarter placements are what's going to drive growth. The study also pegged the total universe of podcasts at 90,000.
Unfortunately, for all you indy podcasters out there, this does not bode well. With all of that competition for ad dollars, the money is going to flow to folks who have ad sales reps. This means mainstream media podcasts and podcasting networks will benefit most.