Kate
Most popular groups/organizations/clubs/teams on campus are club field hockey, club lacrosse, Student Ambassadors, sororities, fraternities, Saferides, and the University Program Board. A group I am involved with is the Nursing Students Association, we have bimonthly meetings, fund raise, plan community events, and volunteer in the local area. Students in dorms leave their doors opens sometimes, it depends on if you like your neighbors. Athletic events are pretty popular, as are guest speakers and the theater. The dating scene is pretty much what you would find at every college, nobody is looking to be tied down, unless they came to college w/a girlfriend or boyfriend, have a g/f or b/f at home, or aren't a freshmen, a lot of the guys are players and jerks, and a good number of the girls are sluts. I meet my closet friends through classes and through where I live. If I am awake at 2AM on tuesday I am shopping online or laying in bed. Traditions and events that happen each year are Homecoming, and football games. People party pretty much every weekend. Frats and sorotrities aren't that important, you can still meet people if you aren't in one, BUT a lot of people like them b/c they build close relationships with a tight knit group of people. Last weekend I stayed in, I'm sick. On a Saturday night you can go to Taylor Down Under and play pool or listen to music, go to Grafton Stovall and watch a movie, go to UREC. Off campus you can go shopping at the mall, target, or the Wal-mart shopping center, you can go to the apartments on the weekend.
Jamie
Some of the popular organizations are: University Program Board (UPB), Student Ambassadors, SafeRides, Orientation volunteers, Make Your Mark On Madison (MYMOM), Outriggers, Homecoming, Student Duke Club.
I'm in SafeRides which is a really fun organization. Our main mission is to educate students about the dangers of drunk driving and we also provide rides home on Friday and Saturday nights. SafeRides neither encourages nor discourages the consumption of alcohol so it's nice to have an organization that provides useful knowledge and help without being "preachy." Also, the club has a lot of excited members so it's really something you want to do, not something you feel like you have to do (like giving up a weekend night to work).
My suite always left our door open in the dorm.
Athletic events are very popular, especially football games and basketball games. Guest speakers are also popular, we've had a lot of interesting ones this year, Rev. Desmond Tutu, for example.
The dating scene is a little tough since there are more girls than guys. Still, many people have boyfriends/girlfriends.
Greek life isn't huge, I think it's only around 11 or 12 percent of all students.
Traditions that happen every year: throwing yellow and purple streamers at football games, Sunset on the Quad during Homecoming, Grilled Cheese Thursday at DHall.