Hi there,
Short term is certainly unique, but the opportunities that exist within it are quite varied. There are classes that are really academically intense (ex: "Math Camp" aka Introduction to Abstraction), classes that are abroad or travel within the US, and classes that are less textbook-y and more hands-on (ex: "Varsity Recess" aka Methodology of Coaching, Introduction to Archeological Fieldwork). A few majors (history, politics, and math among them) require a particular short term course, but other than that, it's pretty much a wide-open choice. You can also always propose an independent study, which can be about pretty much whatever you want. Short term, like most things in life, is what you make of it. Some people plan their short term to be a time of taking a class outside their field of study for fun, some (especially seniors) plan it to be primarily a last hurrah/relaxing/going to the beach/partying time, and still others use it to secure another credit in their major.
If you're interested in looking at some possible short terms, besides the ones I mentioned in passing, you can go to the catalog,
Bates College Catalog: 2009-2010 PRELIMINARY, click on a field, and then scroll to the bottom. Short term units are the classes with the "s" (ex: ECON s21).
I do know a few individuals who have completed their studies in 3 years, and I can only imagine more and more students will be interested with the current economic situation. It's definitely do-able, and the people I've known who have done the 3 years have done just as many extra-curricular activities as those going the traditional 4 years. So you can definitely do it and still have a life, which is always nice.
Hope that helps and doesn't hurt! Let me know if you have any further questions. I can also get you in contact with someone who's doing the 3 year program if you'd like -- he works in Admissions as a tour guide so he'd be thrilled to talk about Bates and his experiences.