To be completely honest, I'm not too great at group studying. It's hard sometimes with Writing Seminars and English, because a lot of our assignments are either creative writing or reading a selection from a book that you can't really focus on unless you're working on it alone. It really helps to get together with other people though to do homework assignments that "work" in a group setting. I actually have a Fluid Earth date tomorrow night during Top Model with my roommate and my neighbor so we can finish our homework questions for that class that are due Friday, and those work well because it helps to discuss them with others and get more than one brain contributing to the answer. :) I think it helps to have others there with you, both because they can help you on things that you don't understand, and because it feels really good to be able to commiserate. It isn't healthy to complain all the time about a class or work, but it's definitely a comfort to have other people to work through problens with.
Oh, also, before finals it helps to get together with one or two people from ANY class you're in to discuss what you worked on over the course of the entire semester. This might also work better for natural science/engineering students, but social science and humanities students will also benefit. You can't possibly remember or keep track of everything you did in three months, so it helps to bounce ideas off of someone else and prepare an outline/list of things you should study.
What's great about Hopkins is that you can pretty much go either way. If you work better in a group or want to try it out, a lot of people are willing to study together. If you work better alone, most of the time you'll be able to do that as well {unless you're given a partner/group project}. It's your education, and it's totally up to you!