For those of you applying, here's a quick "insider" view of the cohort and learning team system at Wharton.
Cohorts are simply groups of students, basically put. We are 800 students, and are divided in 12 cohorts of roughly 60 - 70 students. You take all your core classes with your cohort. The cohorts are created by the school's administration: they claim to put a lot of thought in diversity in terms of previous jobs, geography and gender. From what i gather they have actually done a pretty decent job (except that there is a cohort with an abnormal number of hotties, and of course I'm not in it

).
Inside that cohort, you will be divided into learning teams of 5 or 6 students: all the teamwork will be done with that learning team. Again, there are rules when they create these learning teams: there will always be at least a girl in each group and at least an international student (my group is composed of 4 guys and 2 girls, one of the girls and I are international, although the girl actually lived in the US for quite a while).
Now there are pros and cons to this system: the pros are that you get to meet people quite quickly and easily. You'll know the people from your cohort very well, but you'll probably not know other people from other cohorts very well (more on this further though). This creates a sense of community and it's a nice and easy way to get to know people. People do a lot of stuff together and that's nice (like cohort B-Day celebrations, dinners, drinks, excursions, etc). For example my best friend here is in my learning team (again, more on this later). The learning team principle is also a great way of learning to work with people you don't know at all and who come from very different backgrounds and have different working styles and aspirations - this might sound like bullshit but it's true, trust me.
Now the cons: well, the cons are pretty obvious: if you don't like your cohort, you're pretty much f***ed. But to be honest, if out of 65 people you don't like anybody, you're most probably a weirdo. Also, some might argue that they don't the idea of getting to know 60 people very well and not knowing anybody else. That's a valid point, but I disagree with it: if you're not going to get implicated in anything, then yes, it'll be a problem. But if you get involved in stuff that you like (sports, professional clubs, the opportunities are litterally endless) then you'll meet by efinition other people from other cohorts with the same interest as you. In my case my best friends here are part of the rugby team and the soccer team. The guy on my learning team plays both like me.
Now more on the learning team: as mentioned previously, the learning team principle is also a great way of learning to work with people you don't know at all and who come from very different backgrounds and have different working styles and aspirations. And believe me, people will be VERY different: some will not really care about academics and just want to get involved in EC stuff (sports, pro clubs, partying, whatever) - this is me and my mate - and then you'll have people very focused on the academics. Sometimes working in that kind of environment is challenging, but you do learn a lot in terms of compromises, etc. It's actually harder IMO than the professional environment, because (in theory) everybody wants to do well in their pro lives; over here it's not the case (if you compare academics with professinoal success) - I hope you're catching my drift.
Now the cons for the learning team principle are the same than for the cohort: if you don't like the people in your learning team (and that can certainly happen, as opposed to your cohort), you're doomed to spend a **** year on the academics point of view. Some claim that there's a lesson to that - working with people you don't like - and they have a point. But that doesn't improve you life now does it? This unfortunately DOES happen, I've heard some (not a lot though) horror stories. The good thing is that these learning teams are constantly monitored by 2nd year students that are trained for that (and they globally do a good job). My team is great on that point of view though: we managed to find a good balance despite the (very) different aspirations and we work very efficiently together. Moreover our team got closer over the months once we really got to know each other, which is nice (crazy nights around the blackjack and poker table in AC did help though).
Another con of the learning team is that you might have an alpha male or female trying to dictate everything in the group. Trust me, this WILL happen is some groups(this is Business School after all, there are a lot of alpha types around). It's tough to manage those kind of situations, but it's a learning process I reckon (but it still doesn't make your life any better).
All in all, I'm in very favour of both the cohort system and in favour of the learning team system (although less). I guess it's like in everything: there'll always be bad experiences, but the benefits of this system outweigh the inconveniences of the minority.
Anyway, I hope this helps! If you have any other questions about this stuff or if there's points I haven't covered, shoot away.
PS: sorry for the (very) disorganised post, I can't be arsed to improve it.