The Tenderloin is a downtown San Francisco neighborhood that is pretty sketchy and seedy. In fact, that’s part of its charm. Still, the (comparably) cheap rents make it attractive to a broad demographic, psychographic, and just plain psychos. A few months ago, Adam Jackson, 22, moved there and was surprised by the crack deals, violence, and general rabble-rousing outside his window. So he and his girlfriend set up a couple Web cams and a site, AdamsBlock.com.