Several years ago I started a Joni Mitchell Guitar site in conjunction with the Joni Mitchell Discussion List website. I worked with three other musicians to build this thing into a monster database of Joni's tabs. What is very interesting about this site is it teaches the musical student how to acurately play the song in Joni's original alternate tunings. I'm very proud of this site so if you would like to check it out, go here:
I have ideas about someday doing a podcast related to Joni's music, but I'm not sure how to do that yet so I'll continue to explore.