I still love Fleet Week, but if I were to fly back to SF at this time of year it would be for something entirely different: the Hardly Strictly Bluegrass Festival. One of the largest music festivals in the country, set up in Golden Gate park and drawing crowds of 600,000, the Hardly Strictly Bluegrass Festival has an all-star line-up and, quite simply, some kick-ass music. Robert Plant, Gillian Welch and David Rawlings, Steve Earle, the Preservation Jazz Hall Band, the Punch Brothers, Merle Haggard and Kris Kirstoffersen, Emmy Lou Harris, Patty Griffin, and, on the really hardly strictly bluegrass category, Bright Eyes, M. Ward and Broken Social Scene. (Rolling Stone has a fun write-up.)
It was started in 2001, funded entirely by a billionaire with a love affair with bluegrass, and riding the waves of interest in bluegrass and roots music that followed the release of O Brother Where Art Thou. A few years later it expanded, including more folk/rock and blues, as well as that twangy New Orleans Jazz (hence, "Hardly Strictly Bluegrass"). When I attended in 2003 and 2004 is was still a little scrappy. You could come by 20 minutes before an Emmy Lou Harris set, and still get a place to sit.
Now it draws huge crowds, and even people who try to camp out over night. And every year I wish I had flown home just to attend! Luckily, there's always youtube: