Skidmore is a very, very social place.
The most popular groups on campus I would say are the acapella groups/ musicians, as well as the comedy troups. Athletics, not as much, but I've heard they get a good turnout at games. Theater is pretty big at Skidmore, and there are a couple of shows a semester.
The dorms are a great place to meet people. Apart from Wiecking Hall, all of the dorms are suite style and opening up onto one big hallway, so it is simultaneously private and social. Kids leave their doors open, and there are always people around to hang out with. There are common rooms on each floor, and all the dorms are pretty close to each other. Once you're an upperclassmen, you live in Scribner or Northwoods, 2 on-campus apartment complexes which are 5 minutes further away from the academic buildings. Scribner is extremely social, with houses that hold 4,5,6, or 7 kids. It is like a neighborhood, with many different units and houses. At nights and on weekends, there are parties and concerts in Scribner, and there is always somewhere to go off campus as well. Skidmore doesn't have greek life, but many of the sports teams and clubs have off-campus houses, and they usually provide nightlife for students.
Also, Caroline Street (off the main road) has many bars and clubs for the 21+ crowd, and a new club The Grotto just opened up with 18+ nights. There isn't much pressure to go out and party, though. Plenty of kids hang out in dorms or in the Spa or Case Studen Center at night, where there are often comedians, concerts, movies, or speakers. There's something for everyone.
Skidmore's got some great traditions as well. On Halloween, there's MORBID- the halloween dance. It's the one night the entire school gets dressed up and has a good time. It gets a little crazy, yet it is easily one of the best nights of the year, and everyone looks forward to it. Also, in the winter there is Junior Ring, a semiformal dance, which again most people go to. In the spring, there is Fun Day! There are moonwalks, dunktanks, booths, carnival foods, and the best part is that it is OUTSIDE IN THE WARM WEATHER. The entire school goes out and hangs out on the green. It is at the end of the semester, so it is a great way to destress and let your inner kid come out again.
There are also 2 big concerts a year put on by the entertainment committee. Often its a big name act, and again most kids go to those. There's something for everyone.