Pros
Princeton is a beautiful campus and a rich academic environment for a graduate student. While the campus social activity is certainly more directed to the undergraduates, the Graduate School really does try to provide many events and avenues for grad students to have fun outside the lab and classroom. The proximity to New York and Philadelphia is great, too. The academic environment is challenging - but provides a good community for support and growth. The financial support for PhD student is excellent compared to other schools.
Cons
The academic environment can be overwhelming, and at times feel like there isn't structured support at the department-level for graduate students. Groups of students in departments or between departments, or a mentor besides one's advisor can be helpful. The housing situation seems to be changing for Graduate Students, and finding affordable housing can be tough in an expensive market.