Campus life at Bowdoin is seriously what you make of it -- I know so many people, including myself, who have complained that there's nothing to do on a given weekend and then another weekend I've actually gone to see the entertainment Bowdoin provides or the student theater productions and it's been great. We usually have a few really good speakers (last year, RFK Jr., this year, Eve Ensler from the Vagina Monologues) and a few good bands (Ben Kweller this year). There are also things like Thursday pub nights, where they'll get a live band or a DJ and you can go dance.
Student groups on campus are somewhat popular. There's a group for pretty much anything you could want, and it's easy to start a club if what you want isn't offered (which I did myself), but in general Bowdoin fits the norm of extracurriculars decreasing significantly once everyone stops trying to pad their college resumes. The most popular campus groups are community service oriented -- there's a lot of tutoring and mentoring that goes on, both on and off campus.
The dating scene at Bowdoin is pretty standard -- either you're hooking up or you're married. Bowdoin does its best to encourage dating, though -- they'll offer coupons to Brunswick restaurants during "Date Week" and they had speed dating this year.
There is a lot of drinking, but given what I've heard from friends of mine at other schools, it's nothing overwhelming and I have NEVER heard of anyone getting slipped something in their drink. If you're looking for weed, you will be able to find it, but otherwise it's not that prevalent, and I've only heard of about four people on campus who do cocaine. Like I said, Bowdoin doesn't permit hard alcohol on campus, so if people do that it will usually be in rooms behind closed doors (unless they're stupid, and then they usually will get caught).
For underclassmen, the night life pretty much revolves around the non-exclusive coed social house system (Bowdoin got rid of frats eight years ago). Almost every weekend, one of the eight social houses will throw a campuswide with a theme and people will usually go to that. The social house parties are almost entirely freshmen and sophomore, though -- upperclassmen will go to the tower or to the off campus apartments on Pine Street or Harpswell Street.
There is very little pressure to drink, other than the pressure of being bored while you're sober in a room full of drunk people. If drinking isn't your thing, there's a very active chem-free scene full of people who are very gung-ho about being straight edge. A few of them are judgmental, but most of them are cooler than half the people who do drink. They have a social house of their own and throw chem-free parties there all the time.
As for traditions, there aren't a ton because the social house system is so new, and there is no hazing or initiation for the houses because the turnover is extremely high (almost no juniors live in social houses). However, one house always has the toga party, another always has the '80s party, another has the haunted house, and another has the blacklight party.
Ivies Weekend might be Bowdoin's longest running tradition. Though it supposedly celebrates the weekend that Bowdoin turned down the invitation to join the Ivy League, the real reason is that the ivy on the dorms was planted the last weekend in April. There is always live entertainment (OK Go two years ago, Kevin Little last year) and a big "Pinestock" party with campus bands and lots of kegs. It is completely possible to go that entire weekend being drunk or high the entire time you are awake.