Although much research has examined usage behavior of specific categories of websites and the antecedents and outcomes of different e-marketing factors for online user behavior, a proper general framework which serves the purpose of assessing how users interact with the Web 2.0 is still missing. To address this insufficiency, the current study develops and empirically tests a theoretical model that explains the determinants of Active and Passive user behavior on Kijiji.it, the Italian leader of online classifieds. The model has been tested with 628 questionnaires distributed in June 2009. The results indicate that Active use is positively influenced by four independent variables: ease of use, perceived trust through the site and its users, sense of community, involvement. Passive use is positively correlated with six independent variables: the four above mentioned plus the functional characteristic of the site and Enjoyment.