Gregory James bought his house way back in 1972. As he looks around at the stone-fronted rowhouses that line either side of his street in the Mt. Airy section of Philadelphia, he considers himself a relative newcomer. Out of 72 houses on the block, he counts 15 that are still occupied by the families who were already residing there when James arrived. Back in the 1970s, this part of Philadelphia was a choice neighborhood for middle-class blacks who were able to move themselves out of rougher parts of town.