I looked at the website for the Sonora festival that pdq posted. Of the 5 acts in the 2009 lineup so far, everyone is white. Of the 22 performers listed on the homepage under "past festivals," 17 are white (or fronted by whites). (And Bo Diddley is now dead.) This is not a knock on the Sonora festival. That looks like an event I'd enjoy, and the SF festival booked plenty of white artists over the years.
But it sure says something (but what?) about whether or not young blacks are taking to the blues. I know there are black blues artists working today, but I'm not sure if there's a critical mass of young blacks doing it in sufficient #s to make this look like a black vernacular scene. Is this good, bad, or indifferent? I don't know. I listen to white blues artists, and the white Charlie Musselwhite, for one, is as steeped in the genre as a man could be.