If you should see his name come up and consider taking his class, don't. He was visiting Spring 2012. Exams are quite challenging, grading is pretty unreasonable, and he reads from slides so you can skip lecture, which I consider to be a terrible use of $4,000 and 10 weeks of one's life. Full disclosure, I'm in GS with all A's in econ. I got a B+ in the end but nearly 100 on all the problem sets and worked my tail off for the exams. No idea how you get an A but I have never consistently fallen asleep in a class at Columbia before this so aside from being surprised by the grade in the aftermath, I was fairly disappointed with the whole experience. It was a large lecture class but the attention from the TA's was lackluster and certainly didn't make up for the subpar leadership.