Vandy: Probably the most friendly and social people I met at any school. Seemed more "normal," maybe a little less intellectual than at other places.
Pitt: Great students. Everyone I met there was really neat.
Michigan: The school didn't seem to have a coherent personality. A lot of people seemed to do their own thing and weren't as close to each other compared to other schools. But I got along with everyone I met really well.
Baylor: Similar to Michigan.
Columbia: This school probably had the most distinct personality of any school where I interviewed. Very friendly, energetic, good at talking, ivy types (and I don't mean this as a bad thing, but more of a intellectual, on-edge personality). Definitely a place where you either fit in or you don't
Hopkins: The only school where I had a really negative reaction to the students. I thought they, without exception, were pompous and singularly focused on the school's prestige in a self-conscious way. They may be cool when not talking about Hopkins, but I think that let out the worst...
Duke: Mixed feelings about the students here. Some very nice, some a little outwardly arrogant.
Penn: Great group. My student interviewer told me that they looked specifically for "normal" students, i.e. people who like to hang out and not always focus on building refugee shelters, etc. Two of the people I met for an extended period of time during the day were very obnoxious (actually, the most obnoxious person I met during this whole process was a MS1 here), but everyone else seemed great.
Stanford: Very cool group, very relaxed. They are huge on attracting hispanics (and do a good job of it), so that's another factor if you are looking for it. What you would expect from a California school.
Harvard: Not so great. Very "uppity" in general. Not bad, but just not the type of people I would like to be with for four years.
Yale: Probably the best group of students. Relaxed, self-confident (but not self-consciously and outwardly so), comfortable, and VERY friendly. No one seems to have a chip on his/her shoulder and the school seems to bring out the very best in their students.
WashU: I liked the WashU students as well. A little more quiet and not quite as approachable as at other schools, but they seemed really friendly.