I was given an initial on-campus interview, followed up by an office visit involving dinner at a Partner's house followed by a set of three interviews the next day. In discussion with my classmates it really does seem that what they are really looking for is people with whom they can spend time with comfortably. Be the most personable, sociable version of yourself. Get to know the people you talk to, both at socials and at interviews. If you find someone uninteresting, it's your job to keep learning about them until you find something interesting.