I recently ran across one article about a Purdue University prof that is actually creating videocasts. While I think that this is a great use of time and technology, I have to wonder when it stops paying off.
It takes time to create a podcast, don't kid yourself. Our weekly 45-minute podcast takes about 3 hours to produce. Videocasts are even more demanding and depending on how you intend to use the podcast, it may not be worth it.
If the podcast is being produced in order to provide a means to rewind and pause the show in order to enhance learning, then this time is well spent. However, if the podcast is being produced in order to free up the time taken up delivering the content in other ways, there's definitely a point of diminishing returns somewhere.
Once you've hit your stride with podcasting, take a look at what your intent was in the beginning, what your intent is now, and assess whether podcasting is delivering on that intent.