If you record it, they will come...

At least, if you're recording podcasts. A new study by eMarketer has found that the U.S. podcast audience rose to 18.5 million in 2007. It is expected to hit 28 million by the end of this year and 65 million by 2012.

Where the eyeballs -- or ears, in this case -- go, the dollars will follow. eMarketer sees podcast-related advertising in the U.S. more than doubling to $435 million by 2012.

A number of factors are driving the growth of the podcast-user base:

* Greater ease of consumption for podcast content
* Growing awareness of podcasting
* Terrestrial radio’s use and promotion of podcasting
* Increased penetration of portable players
* The evolution of smart phones and proliferation of affordable mobile data plans