Which definition would you give to "penpalling"? Some people might consider it as a hobby, others a way of communication between two people or even an exchange of handwritten papers between two people living far away.
I guess that when you first start writing letters you do it to stay in touch with a friend you met on holidays or to practise a foreign language you are learning at school. Probably we are speaking about a hobby (or a need) at this point. With time you realize how much you learnt about other cultures, customs and countries, how everyday life is for other people far away,… It is so interesting and beautiful to share little details which, otherwise, we would never learn in books, touristic guides or magazines. Also you start sharing personal topics, stories, ideas, thoughts, confidences… which end up building a longterm and close friendship with your penfriend. Sometimes you even feel and/or build a closer friendship with your penfriend than with local friends we are in physical contact with.
So, I would assert that penpalling is more than a hobby in the end. Despite all of us have suffered bad experiences, the positive part about it is much more important. It is so rewarding and brings such a wonderful feeling of joy that in my opinion penpalling is an art!
If you are looking for advice on penpalling check: "Tips on letter writing".