In response to Catherine's questions -
Actually, funnily enough, the classes that have most changed the way I think about the world have more often been lecture classes than seminar ones. I think that the university and professors (and students even!) underestimate the value of lecture classes, or overestimate the impact that seminar-style teaching has. I think that the reason why seminar classes are often considered so highly is because, to be honest, with smaller class sizes and required discussion, students actually have to attend all the classes, pay attention, and do (most of) the readings. However, in lecture classes, if one does the readings, attends classes, and engages with the material intellectually, a student can learn just as much and be challenged in their preconceptions just as much as in a seminar-style class. (In fact, most lecture classes have "discussion sections" anyways, which allow for some discussion with your peers.) Yet, this is not to say that seminar-style classes have benefits - especially for certain subjects (literature I think is one), smaller class sizes and more discussion is better for the student than is a lecture-style class.
In general, though, I think that it is not the style of teaching that matters as much as the quality of the professor. In Columbia, there are professors who are great, professors who are average, and professors who are below average -- just as any other university or college. Most students recognize that it is the professor that makes the class, and certain professors' classes are more popular than others'. However, professors are not necessarily "great" if they are highly respected academically as scholars: the greatest professors are those who are both well-respected and knowledgeable in their field, and skilled in conveying complex information in an understandable and interesting way and leading students to question their preconceptions and consider issues on a deeper, more complex level.
It is these professors, then, regardless of the style of the class or the amount of student participation, that have impacted me so greatly. Of course, I have learned from my peers a great deal, including a great amount of things about other cultures, regions, and viewpoints. However, this learning takes place both in classes and outside of classes (for me, it has been largely outside of class, in extracurricular activities or just everyday conversation). Classes are the opportunity to learn from some of the foremost scholars in their fields, and if those foremost scholars are great teachers in addition to great scholars, then their impact on students' minds can be huge.