I have decided to go to Columbia. I have been concerned about graduate student disaffection. I don't go into it with the illusion of its imperfections (I am very cynical). If your decision is between Ann Arbor and Columbia, one issue may be funding. I didn't look at Michigan so am clueless about the situation there, but I am turning down four great public programs over funding. There is no place where graduate funding in the humanities is going to be "great" right now, but Columbia is relatively good about it in my book. This is key for why I chose it.
Some of the current students did in fact seem a bit unhappy. A recurring source of complaint was the university's bureaucracy (that said, they processed my travel reimbursement with startling rapidity). I would imagine that when you go into the program, you have the academic challenge (true everywhere) but also (if you are from outside NYC) the unique dilemma of having to figure out this immense and complicated city. It's an obvious point, but choosing to go to Columbia, or NYU, or CUNY, or New means choosing to live in New York City. The city and the university are inseparable. I hate those types who think that anywhere but NYC is somehow "beneath them". But the location does matter.
That said, I think it is a fantastic department and I really liked the faculty members I met.