This may seem ironic having spent all my working life in broadcasting but I have really mixed feelings about the current rush towards audio-blogging and video-blogging.
To me they are both, in many cases, much less efficient than text. With text I can scan, I can jump sections, I can glance away for seconds without interrupting the flow of meaning and so on and so on. With audio I have to go at its pace. I have to wait for some tedious podcaster to witter for ten minutes before he gets to the point - without even being sure sometimes that he is going to have a point! With video I have to stop what I am doing and look at it.
A case in point is David Weinberger's video announcing his intention to video blog Supernova. To be fair to David I know he is just playing around with the medium but it does show up the issues.
In order to know what was in the video I had to start watching it - unlike text where I could scan and get an idea of the content before deciding to invest time in it. Despite David's obvious visual charm I have to say I stopped watching after a minute and just listened to the audio as I went back to surfing other blogs. Even doing this I still had to give the audio more attention than I wanted to make sure I didn't miss anything and ended up half surfing , half listening.
At the end of the day the video was simply imparting factual information that I could have got better from text - including the hyperlink that David had to hold up scribbled on a bit of paper and speak two or three times in case I missed it!
Audio and video can seem sexy and fun, and there is little doubt that the web is an amazingly powerful way to distribute video and audio content and will change the media world for ever, but it is more a case of using the most effective tools for each job and I guess that is something we are all learning.