I addressed what to expect in terms of work loads in the other version of this thread. In terms of study habits, well, it varies. Depending on the person and the course of study, it is very diverse. Generally, though, everyone does the work. I don't know of too many cases where people just blow stuff off completely. Weeknights are generally spent working on stuff (but not constantly, IM sports, other activites, or just being social happen, too, but at least some time will get spent on some classwork). From Friday afternoon through Sunday morning, work becomes rare, expecially at night. Sunday is often the day people spend getting stuff done, especially things that require a long block of time.
These are just general trends. Very few people study all night Monday-Thursday, and then all day Sunday. But very few people don't touch a book during those times either. It's about balance, basically. It is pretty rare for someone to completely blow off their work. It's also rare for someone to get stuff done way ahead of time.
Also, Four classes is very manageable. I've known a lot of people who've taken three and been bored.