Bowdoin is very diverse for a NESCAC school, but that's pretty faint praise. A Bowdoin professor actually wrote a book called "Why Are All the Black Kids Sitting Together in the Cafeteria?", although she wasn't referring to Bowdoin specifically. There are some social groups along ethnic lines, but there are also plenty of people who are friends with people inside those groups and there's never been any tension between them. The LGBT community is small, with a lot more L's than G's. Whether you think Bowdoin is accepting depends in large part with who you hang out with -- the women's rugby teams and the theater program would probably say their friends are extremely accepting, the football team maybe a little less so. No one who's out gets harassed or made to feel uncomfortable if they're out, but I think that at such a small school, coming out is a big enough deal that a lot of people wait until after graduation to do it. All these different types of students definitely do interact, though -- the more you get involved with extracurriculars at Bowdoin, the more diverse you realize it is.
Most Bowdoin students are from New England; 25{4a082faed443b016e84c6ea63012b481c58f64867aa2dc62fff66e22ad7dff6c} are from Massachusetts alone. A friend of mine at another school told me they had a "Rep Your State" party and I told her Bowdoin could have "Rep Your Town in Boston Metrowest" with the same number of people. That said, there are a ton of people from the tri-state area, a lot from Pennsylvania, a lot from Chicago, and a decent amount from the West Coast. There are very few people from the Midwest or the South.
Politically, Bowdoin is no Vassar or Hampshire, but we are still very active. A number of Bowdoin students have gone on to work for College Democrats of America and the founder of Students for Barack Obama is a senior; she now sits on his national campaign's board of directors. There are like, ten conservatives on campus -- I think the rest are in hiding out of shame.
As a public school student, I think it's incredibly easy to tell who went to private school and who didn't, but the class divide is definitely not that simple. There are a lot of international students, a lot of people from wealthy towns with excellent public schools, and a lot of students who are on financial aid. Many of the people I know who are on financial aid are not embarrassed to talk about it at all -- during my freshman year, I was not on financial aid, and I actually was more uncomfortable about admitting that than admitting I'm on it now. Girls actively compare their bargain shopping, which I always think is a good sign that we're too rich and entitled. People definitely would not talk about how much they'll earn one day -- even the ones who will earn millions would never be that crass. There are people who will namedrop or talk a little too much about their vacation house(s), but I've been surprised multiple times to find out that someone completely down-to-earth is one of the wealthier people I know.
There's only pressure to dress up for class if you don't like being in the minority wearing sweats, but no one is going to stare at you if do -- especially in the morning. I will say this, though -- I didn't know much about designer jeans before I came to college, and now I can recognize almost all the major brands; I think they osmosised into my brain. There are a few girls who will wear heels to class, but I think everyone kind of agrees that they look like idiots.