I'm replying to this thread quite late I realize, but as someone who has visited San Francisco quite a few times, but not within the past 10 years, I'm curious about a couple of things, too. Interestingly, I stayed in a place called The Bijou hotel which was right on the corner where the Tenderloin started. The video that's posted here of the Tenderloin doesn't look that bad at all to me; in fact, the Tenderloin looked scarier when I was there in 2003 and 2005 staying at that same Hotel than it does in his video. He should go to Kensington in Philadelphia if he wants to experience shocking street life.
I wanted to ask native San Franciscans about Buena Vista Park. I had quite a bit of fun there on every one of my trips, but I do know that quite a few homeless people hang out in there, and so I'm just curious if it's considered a dangerous spot to walk either during day or night now? It's a beautiful place.