Is podcasting lectures a good idea?
On the face of it, yes of course! It opens up what is being said, and the discussion, to anyone anywhere in the world. It's freedom of knowledge and information etc etc, and one of the real benefits of the internet.
And people have asked whether the conference I'm currently attending in New York (on new directions in ancient history) is being podcast or posted on the web. Answer: no. For good reasons, I think.
It's meant to be a free and frank discussion of where people think ancient history is -- or should be -- going (and I've already been rather too frank for comfort, I'm afraid). And the organisers felt that it would dampen the discussion if a record of it was preserved for posterity, and in fact there to haunt the poor speakers ten years later when they might have changed their minds anyway ("But in 2012, you said....")
I've felt a bit the same about having lectures podcast, but for slightly different reasons. That's to say, you accept an invitation to lecture somewhere and sooner or later the request comes, "I hope you dont mind if we podcast it.." And it looks ever so curmudgeonly to say "well yes I do actually".
The point here is two fold. First, it means that you cant give the lecture anywhere else again. Otherwise you risk the organisers at your next venue googling you to get the material for their introductory words and finding .. guess what? Yes, the full version of the lecture you are about to give them, as given a month ago at some other university.
Second, there's a more intellectual aspect to this. When you go round to different venues giving more or less the same talk, that isn't laziness. You do it because the reaction that different audiences have is actually helpful in making it better, getting it ready to publish. Only delivering it once actually limits the response that you need!
I sometimes try to say. "Well OK, but can you only have it on the web for 2 weeks". But I suspect that it never is really taken down (and even if it is, it probably lingers somewhere in cyber space).
Maybe someone more technologically competent than me knows how easy it is to live stream something in such a way that it cant be "preserved" beyond the moment. That might be the compromise between open access and repeatability.