About a year ago, I enrolled in ENGL 151 online at my college - it's a fairly advanced composition class. I was supremely disappointed in the online instruction site, the "depth" of the class and so I dropped it fairly quickly. The next semester I took the same class with the same instructor - but in the actual classroom.
The improvement was incredible - The teacher was approachable, insightful and the campus class was far more enriching than the online course. All because of the face-to-face interaction.
While a student obviously needs to be responsible and motivated in either setting, I think the answer ultimately depends on the curriculum. Objective courses like economics would probably do well online, where subjective courses like Essay Composition suffer from the limitations of online forums.
My 2¥.