This question refers to the work The Death and Life of Great American Cities (1961) by Jane Jacobs.
In her text, Jacobs argues that having buildings with easy access to the sidewalk and the outside encourages people to be more engaged with the street. In turn, this encourages them to interact with neighbours more often, and to pay attention to what goes on outside. The people watching are the "eyes and ears upon the street," which can help reduce crime and increase the quality of public life.
In the years since the book was published, cities have changed in important ways. However, I do not believe any of these changes affect Jacobs's concept. Cities are more multicultural now. However, Jacobs's ideas could still be applied in that context, and in fact, are likely to encourage the integration of immigrants. Economic inequality is also not a significant issue, as the use of the street and the interaction of neighbours does not necessarily follow economic lines. Finally, the variation of personal behaviours is not a new phenomenon, as people have always have very different behaviours and habits. However, this does not necessarily mean that they cannot interact as neighbours.