At least for Nob Hill, the location should be high density but low traffic. I think a good block for a food truck to park would be on Cushman Street between Huntington Park (Taylor Street) and the Pacific-Union Club (Mason Street) between Sacramento and California streets.
Chameleon Cafe on the corner of Pacific and Leavenworth had a different food truck come out every Thursday evening during the warmer months this year. It was a HUGE hit, both for the neighborhood and the business. Lots of kids, neighbors getting to know each other. It was great for the business because people would order food and then eat it inside with a glass or two of wine, so everyone wins.