To some of us, this is the passing of an age. Here's an excerpt from his obituary in the New York Times.
Mr. Seeger’s career carried him from singing at labor rallies to the Top 10 to college auditoriums to folk festivals, and from a conviction for contempt of Congress (after defying the House Un-American Activities Committee in the 1950s) to performing on the steps of the Lincoln Memorial at an inaugural concert for Barack Obama.
That's quite a career. I saw him perform with Arlo Guthrie - as he often did - once at Celebrity Theatre in Phoenix. He celebrated folk music. He was one of the good guys. Rest in peace, Pete.