Even setting location aside, some obvious differences come to mind. As an undergrad, I worked hard, but I also had a good amount of time for relaxing, going out, and having fun. I pulled all-nighters to write papers, did problem sets, studied in the library until midnight ... all of which I have done in grad school as well. One notable change is that when I was an undergrad, I thought nothing of leaving the library at midnight and staying out until four a.m., whereas now I am much more likely to do something relaxing after a day of work. I'll pretend that's because I am living in Princeton now and not because I am four years older.
Another big difference is the schedule: as an undergraduate, my workload was tied to the academic calendar, with its midterms, finals, and papers. When the summer arrived, I forgot about school and focused on travel, internships, and relaxing at the beach. In this respect, graduate school is very different. Most grad students at Princeton complete their coursework by the end of their second year and spend the remainder of their time here focusing on research. This difference has its upsides and its downsides. One upside is that we are not constrained by very many University-set deadlines, allowing us to avoid major interruptions in our research; the downside is that we are expected to work continuously throughout the year. Thus, when my friends ask me, "What do you have planned for your summer break? I wish I still had three months of vacation," I have to remind them that although class is not in session, not much changes for me in terms of school. My summer "vacation" plans consist of working on my dissertation... though yes, perhaps from East Hampton.
In the end, the most pronounced differences between the undergraduate and graduate experiences stem from the divergent purposes of these two educational pursuits. As an undergrad, I explored wide-ranging interests, acquired skills, made friends, and thought about life after graduation; now the focus is almost solely on professional development. Graduate education is intended to produce scholars, and the process of working on a dissertation enables (or forces) students to develop an expertise in a particular topic. I no longer have classmates, but colleagues; for those of us who remain in academia, the people we meet in graduate school are those with whom we will co-author papers, collaborate, and compete for jobs throughout our careers. Professors' expectations regarding the quality and intensity of graduate student work are likewise much higher. They have a vested interest in our becoming the most competent researchers and academics possible, as we will be their colleagues and intellectual successors in the years and decades ahead. This is the central focus of graduate education: to develop the skills, knowledge, and competence necessary to be a successful professional in one's field. The skill sets we seek to build may differ from those one might develop as, for example, an analyst at an investment bank, but they are ones which are relevant to our post-graduate lives: presenting papers, conducting independent research, thinking critically, articulating ideas, and being members of an intellectual community.
The focus on professional development is reflected in the lifestyles and demographic composition of the graduate student body. Unlike undergraduates at Princeton, who are often close in age and who are typically unmarried, the graduate population is very diverse in terms of age, marital status, and family situation. Some students come directly after finishing their undergraduate degree, while others work for several years in between; some are single, while others are married and have children; some live on campus, while others live in New York or Philadelphia.
The heterogeneity of needs that arises from this diversity presents a particular challenge to groups tasked with enhancing graduate student life, including the Graduate Student Government (GSG), of which I am the chair. The GSG advocates for the interests of the entire graduate student community, which makes its mission rather broad and its agenda pretty packed. We have successfully lobbied the University for better health insurance, including maternity leave, subsidized birth control, lower-cost dependent coverage, expanded summer hours at UHS, higher stipends to cover cost of living increases, higher e-mail storage quotas, improvements in the housing application process, reduced rents in the Lawrence apartments, creation of DCE status for post-enrolled students, and more funding for academic travel.
When we are not working to improve the campus shuttle or expressing student needs to administrators, we organize a variety of social and networking events - including a Valentine's Day dance, a wine and cheese tasting, student-alumni mixers, research symposia, a photo contest, and an upcoming travel festival - and sponsor student-organized activities through the GSG Events Board. Graduate school can be a uniquely challenging experience, and the GSG plays an important role in uniting the graduate student body, articulating its needs and concerns, and providing some necessary distractions from the stress of academic life.