Learning teams (LTs) are a huge part of the Darden experience. Basically, it is an assigned group of 5-6 people who meet each evening to prepare and discuss the next day's cases. Most LTs meet between 7 pm and 10 pm each evening, although that schedule can vary. My LT, for instance, used to meet at 7 and now meets at 8. Also, I don't think it has ever taken us 3 hours to prep our cases; we're usually done much faster.
Basically, the LT serves a couple purposes:
1.) It helps everyone prepare for class. The cases are not always (or ever) the easiest things to figure out on your own, and by meeting as a team, you're able to share insights, resolve questions, and generally come closer to "cracking the case" (or at least being able to discuss it or ask intelligent questions in class the next morning). Also, once company briefings and networking receptions start (around the middle of Septembre) and you have less time to prepare on your own, your LT should be able to help you get through the material.
2.) It gives you experience working in teams. Basically, this is the point of business school. If you are going to be an effective manager, you need to be able to work in and/or lead teams, and Darden especially is big on having you learn how to do this in a hands-on way.
As I said, my LT is highly functional, and we all seem to get along pretty well (we had dinner together tonight, we've done Wednesday trivia night at the Mellow Mushroom, there's talk of LT apple picking, etc.); not all LTs are running so smoothly. There are some interpersonal conflicts, some conflicts regarding goals for evening meetings (always getting the "right" answer vs. gaining some insight/focusing on the big picture, etc.), some scheduling issues (remember that a decent number of Darden students are married/have children), and other conflicts. While LTs are supposed to stick together through Q3, if your LT is completely disfunctional, you can disband (although apparently you still have to do StratSim together in November... I still don't know what this is, so more on that later). There are also various resources available to LTs that are having problems so that they can try to work through those problems. For instance, our LO professors have offered their assistance, and each LT has an assigned 2nd Year LT Mentor, who are 2nd Year students enrolled in a class on leading teams. They come observe our LT meetings periodically, and they are a resource to whom we can turn to confidentially discuss any team problems.
Like I said, though, my LT pretty much rocks, and I am quite, quite thankful for that, having been on some atrocious teams in the past. Here's to hoping we continue to get along!