Totally agree with Craggy's points.
Like many others here, I found my MA very social, not only on the student level, but also at the department and university level: loads and loads of talks, reading groups and just drinks where faculty and students interacted outside of the usual teacher-student relationship.
I, somewhat naively, thought that was representative of postgrad experience and have, consequently, found my PhD very disappointing in that regard. My department has a deliberately small group of research students, but there is very little in the way of reading groups, talks, drinks (no drinks!) etc, and what there is tends not to be publicized at all, so it is very difficult to find your way to these things as a new student. My cohort of four meet regularly socially, and for a writing group, which is pretty much essential to my mental health, but that's kind of a paltry substitute for a wider intellectual community. With hindsight, I would pay far more attention to the social aspect of the universities I applied to, and try to see through the bull about "friendly, nurturing environments" etc and to try and get a less PR-ish version of what actually happens in departments (but it's so hard to tell this from the outside that I'd probably fail anyway!).