After listening and watching several podcasts I feel that most of the time effectiveness has to do with the individual. This thought is particularly geared toward the topic of the podcast. There are so many different podcasts out there that it can be hard to find one that you like, so if you are listening to one you do not enjoy then you probably do not find it effective. For instance, I like listening to the “Tim Gunn’s Guide to Style” podcast on iTunes but that is probably because I love his show—so people who are not interested in his subject field probably will not like his podcast.
In general I have found that podcasts are more effective if the person who is speaking is well versed and enthusiastic about the subject. There are some podcasts where I wonder if the person has any clue as to the topic so it makes listening to them difficult, but if the person is lively and knowledgeable then it is easier to engage yourself into the podcast.
Humor makes a difference in podcasts—especially the audio ones. In order to keep the audience engaged in what is being said rather than doing something else and playing the podcast in the background, a podcast should have some humor. Humor allows the audience to be engaged and want to hear more because honestly, who does not like to laugh?