This study explored the behavior of students who used a book recommendation system, specifically the My-Bookstore system, over a five semester period. This study addressed two main research questions, the first being related to "the most frequent behaviors and behavioral patterns." The results showed that "visiting" behavior and "book recommendation" behavior were the two most frequent behaviors in the first and last semesters. In addition, there was a tendency for the recommendation behavior to increase over the five semesters, implying that the My-Bookstore system can facilitate the book recommendation behavior. The second research question concerned the influences of "incentive models on the recommendation behavior." The findings demonstrated that the coin reward incentive in the game has a short-term impact on student recommendation behavior. However, those functions that have an internally tightly-coupled relevance to book recommendation (e.g., "choosing recommended books" as a store management incentive, and "checking histories" a social interaction incentive) act to give the My-Bookstore program better long-term effects on the students' book recommendation.