I really don't know anything about podcasting, I guess it is like recording and then getting it to be online so other people can hear it.
Even though it is not very common to use in class, I'm sure it can be of great use in classrooms as a different technique for students to use. It can be of great use for students who learn differently, and it can motivate them to do something different and be more creative.
I guess we can use it for different activities, like recording a drama instead of acting it. It could also be helpful for low grade students, they can read the story as they hear it.