Her particular bete noir during her New York City years was Robert Moses, who was one of the most influential (and probably the single most powerful) proponents of the orthodox planning of the day, and a relentless and politically powerful destroyer of urban neighborhoods. In a major battle over Moses' plans to build an expressway across lower Manhattan, a citizen group led by Jacobs fought him for several years, ultimately defeating the plan and, in the process, destroying Moses' aura of invincibility. Within a few years, he was effectively out of power.
The battle between Jacobs and Moses was essentially a battle between opposing views of Liberalism, with Moses the paternalistic, all-knowing government authority doing what he and his professional cohorts had decided was best for the public, and Jacobs advocating for the ordinary citizens who she believed were possessed of both democratic rights and the ability to ultimately make sensible use of them. I suspect that a major cause of the decline of Liberalism in the late twentieth century was the result of its leaders' failure to grasp the import of Jane Jacobs' destruction of Moses, and their insistence on clinging to far too many of the institutionalist notions of the Moses era.
My own experience of reading Jacobs' first book was interesting. I had been a fan of Lewis Mumford's rather idealistic (and ultimately anti-urban) ideas about planning, which were almost as much at odds with the planning orthodoxy of the day as were those very different ideas that Jacobs put forward. But Jacobs attacked Mumford as vigorously as she attacked the orthodoxy. I was so scandalized by some of the things she said about the Garden City movement (of which Mumford was a major advocate) in her first few chapters that I nearly quit reading the book, but at the same time there were her affectionate descriptions of city neighborhoods of the sort that the Garden City planners had always excoriated, and I knew that the few such neighborhoods I had actually visited had pleased me. I had always thought that such neighborhoods were urban anomalies which had somehow survived despite their obvious violation of the Rules, but Jane Jacobs explained that they succeeded precisely because they violated those rules. I kept reading, and by the time I finished the book, I was pretty much finished with Mumford as an authority on what constituted good urban planning. My final disillusionment with Mumford came when I read an article he wrote on Jacobs and her book. It was the snottiest, most condescending and narrow-minded piece of his writing I had ever read, and it was far more damaging to him than it was to her.
A lot of people must have had similar experiences to mine on reading Jacobs. Despite the fact that, almost half a century after the publication of the book we still live in a world that is the mostly product of the early 20th century planners' ideas, there is now a widespread and active opposition to those ideas. Upon publication of the book, Jacobs became the target of virulent attacks by both the practitioners of planning orthodoxy and the advocates of idealist alternatives, such as Mumford. The resultant publicity helped make her book famous. (A few years later, when she published The Economy of Cities, professional economists completely ignored it, thereby containing its spread. I don't know if they ignored it because economists are more cunning than city planners, or because they are so insular that they believe that no book about economics by a non-economist could possibly be worth mentioning.)
Today, it is no longer considered bizarre to believe that high-density urban neighborhoods of mixed uses are the dens of evil that they were generally thought to be through the 1950's. Today, there is considerable hope that dense city neighborhoods of the sort that have endured for thousands of years will again be able to thrive in the United States, as they have often continued to do in many supposedly backward nations. If the meddling of professional planners is rolled back to the point where American urban life is able to improve and thrive, much of the credit will go to Jane Jacobs.
Here is a brief memorial post by Steven Berlin Johnson, author of Emergence: The Connected Lives of Ants, Brains, Cities and Software, and one of the many people influenced by Jane Jacobs.