Greeks are not a big thing on campus. There are like three frats/froroities (coed), but the people who are in them are in no way defined by that. Parties are mostly put on by the school, which is unusual in that they are awesome and tons of people go. Partly b/c the school serves it's own alcohol. They are really well put together. My favorite is the Halloween dance, Harwood halloween, in a parking garage. IT's crazy, almost everyone from all five colleges attends!
Which brings me to another subject -- the 5-C's. There is always sooo much going on becuase there are five colleges all putting on stuff. You will never lack for something to do. Most clubs are 5-C, so you can meet a lot of people that way. I know a bunch of Pitzer people because sports teams are Pomona- Pitzer, and I am on one.
One cool 5-C club is OTL, or On-The-Loose. They have website, check it out. They just lead a ton of really cool trips all around, like to lots of national parks, rock climbing, hiking, surfing, skiing, and on and on. Oh, and all for free.
REsidential life: Most people live on campus all four years. South Campus is mostly underclassmen, with more traditional hallwayed dorms, north campus is upperclassmen and has more suite-style living. In the hallway dorms, doors are usually open.
Oh, how could I forget! Sponsor groups! When you get in, you fill out this extensive housing questionnaire, and POmona carefully groups you with 12-20 other first-years along with two sophomore "Sponsors," and you all live together in the same hall. Sponsors have no jurisdiction over you, they are just their to be your friend and help you acclimate to college. Your sponsor group is like a ready-made group of friends because you are grouped according to compatibility. I, like most people, am still really good friends with many kids from my sponsor group. It's the best thing Pomona does for freshmen - no need to stand around in the dining hall wondering who to sit with on the first day!
Also, Orientation Adventure is really fun. It's a four day trip right after you arrive on campus and move in, and you make even more friends. I went canoeing on the Colorado river.
Atheltics are not USC-style - Mostly people go to games to support their friends, unless the game is versus CMS, in which case the gym (or pool, track, field) is packed and rowdy.
If I were up at 2am on a Tuesday? Hmm, well that doesn't happen very often, i need sleep! But I could be: studying (meaning I had procrastinated - I almost never stay up this late studying), dancing at Table Manners (the weekly dance Tuesday nights), or most likely talking with friends. I'll always remember freshman year staying up til 3 many nights talking, freshman-style, about, for example, sex and gender inequality.
Some people never drink. For them, a club called That Saturday Group puts on fun non-alcoholic activities. Other drink five night a week (there is an official event every night of the week except Sunday nights). Most poeple fall in between. Wednesday night is Pub, a fun dance party that lots of people attend. Saturdays are more wild than Fridays.
As for dating, everything goes. One-night hook-ups, multi-year relationships, abstinence, whatever.