There was a story in the book about when a friend of his (John Cronin) asked him to come talk to his class Citizen Advocacy in the Evolution of American Democracy at Pace College in 2001. Cronin told the class about the upcoming visit: he said: "We have a real treat coming, Pete Seeger is coming to visit." and then reports - I felt like I was talking to an oil painting - the people didn't know who Seeger was. Of course the class was a big success - Pete had them singing a protest song in 5 minutes and Cronin says they talked about his visit for 45 minutes in the next class.
There's quite a bit of interesting discussion about his musical philosophy such as why singing and performing is what is desirable - not just listening. He talks about folk music and how the way songs are passed on and sung in different styles by region is an important. Some folk musicians sort-of resented the fact that the way he sung a song became the desirable one because he was so popular and thus dilutes some of the point of the folk tradition. (this is my simplistic interpretation/memory of what I read in the book).
At 90 Pete Seeger is still active - singing and protesting.