Have seen John (and Iris, as mentioned) many times. John is of course great. Saw him in I think October at the big free yearly bluegrass festival here in San Francisco - of course his voice is very different, but still enjoyable. He wrote so many great songs that if he had croaked in 1980 his legendary status would have been cemented, in my opinion. Iris is I think one of the greatest living songwriters and performers. Last two times I have seen her have left me *floored*. On 'Sing the Delta,' she took her songwriting to a different level.
