I would love to see the numbers for those as I'm never in front of my computer when I listen to a podcast and I don't remember the ads long enough to followup even when I'm interested in the product.
It's not always about direct action, it's often about brand awareness. If you listen to a lot of podcasts, you'll know the first company you think about when you are in the market for:
- Mattresses
- Eyeglasses
- Creating a website quickly
- online backup
- shaving products.
- Mesh networking devices
It's an old joke that the definition of a podcast is "two or more white guys talking about tech sponsored by Squarespace".
Whether you act right then, when someone asks you to build them a website, your first thought is going to be to point them at SquareSpace.
Since the same sponsors keep buying ads on podcast and most of them have coupon codes to tell them where their customers came from, they have metrics that tell them the return on investment.