I've always been a fan of discussing everything that's interesting, but not repeating yourself. The people at
http://the-odi.blogspot.com/ are notorious for this. I love listening to their podcast, but it's reached 3 hours per week recently. They could shave 20 minutes off if they reduced the length of their introduction and stopped repeating things like where the podcast can be found, thank yous, and so on.
The VGDJ podcast also suffered from this. It was very interesting, but as time went on zircon and pixietricks inserted too many songs into the podcast and a large part seemed like filler.
I'd say to watch how long the first few podcasts were, and if the podcast starts getting significantly longer than that, look over it and make sure that what's being added is just as good as, or better than, what else has been carried along.