According to the Yahoo Buzz Index:
But in checking the Buzz, we found that podcasts haven’t yet made the mainstream. Stuck somewhere in our top 6,000 searches, it’s safe to say podcasting has not reached the critical mass of IM (or even photo-tagging) — yet.
Turns out the top searched term is “Video Podcast.” Number 20 is “This American Life Podcast.”
You’ll have to read the article for the rest.