The Sims 3 community blog has a new Q&A about the upcoming expansion pack The Sims 3 University Life, and it provides some interesting information on what college-going Sims will be able to get up to during their time there.
Like in The Sims 2, university works like travel destinations (think The Sims 3 World Adventures), so when you send a Sim there you will have to play only as that Sim until the term (customisable to either one or two weeks) is over and they return home, presumably to find nothing has changed while they were away. This also means your Sim cannot visit home in the middle of the term or invite people from home to visit them, though they may be visited by paparazzi or aliens.
Sims who want to lower the cost of university can apply for financial aid by taking an aptitude test that assigns them a score based on their previous accomplishments in life. While at university any job they have at home will be put on hold, but they can look for ways to make money on the job board at university. Sims who can afford to do so can take multiple degrees.
Once at university, Sims can join a sorority or fraternity just by selecting one when they move in. They can also “apprentice under the almighty mascot”, though there are apparently no secret societies. There are plenty of new social interactions, but college-going Sims cannot get married or pregnant while there.
So clearly the Sims 3 version of university deviates a little from what it's like in real life, but it looks like it'll still be packed full of different things to do, and well worth Sims taking time away from their normal lives to experience it for themselves.