Here's the link to Yahoo!'s new podcasting search engine. It's in beta stages at this time. You can search for either "series" or "episodes" (or both) containing your search terms. I ran a few searches and my results were mixed. When I just plugged in a broad term -- San Diego -- I got 27 series and 329 episodes! These search results show just how broad the podcasting community is. I received hits on podcasts ranging from religious "words of encouragement" to San Diego weather, to sports, to travel and the like. I had less success in trying to find podcasts about "camping in California" (which is what I plan to do this weekend). I received no "series" results and just 3 episode results, though none were relevant really for what I'm interested in (perhaps this just means there are none out there -- can that be possible?!).
For beginners, the "getting started" pages are useful.
I would love to hear what others experiences are with the Yahoo! search, especially as it compares to others like Loomia, PodSpider, SingingFISH, PodcastAlley, or any of the other search engines discussed in this list from masternewmedia.org.