I just came across this doc about John Mayer (get rid of your prejudice if you judge him by his comercial records, he's one HELL of a blues player and does a great job with Bob Weir picking up where Jerry Garcia left off). Very well produced and directed. It's entirely from Mayer's own perspective and he narrates it himself.
Full of great references and quite a nice cut for guitar lovers.
It's available on youtube, in the director's own page (Eastwood Allen), it's called "John Mayer: Someday I'll Fly"