Before entering the university, They doesn't have enough money to enjoy their free time. So they try to find not only the most cheep but also the latest fashion place. I think that there are many good place for young student in Myeng-Dong. When I was high school student, I went to there to eat the cheep and delicious food and to buy brand-new clothes with my friends in almost every weekend.
During the life of university, They have many things to buy, experience and study. In Gang-Nam, There are various kinds of stores, academic places and cultural sites. Especially, There are most good english hack-kwons in Gang-Nam. So A lot of university students who want to improve their english skills enroll on english courses of them in Gang-Nam.
After graduating, They may get a job and work in Jong-Lo. Because most working places are in Jong-Lo. It is very convenient to use public transportation in Jong-Lo. But the traffic is really bad during rush hour. And many office workers enjoy their free time at kind of bar with colleagues after working hours. So there are many bars, pubs and some places like that.