In this paper we present CLIO an urban computing system used to form and interact with the collective city memory, formed by shared citizens' recollections. Our goal has been to study the impact of such a system on the urban culture and in particular how it alters the city, the perception of people about the city and the communication among people. We applied CLIO and conducted user studies in two different cities, in Greece and Finland, personal memories were collected and context annotated through a storytelling process, people were invited to access CLIO via various interfaces and we observed their reactions browsing collective city memory and their interactions with our system. Our experience shows that urban computing applications can have a strong impact on city culture and people perceive the important role of such applications in the urban life, it is revealed that smartness is a salient aspect of a successful urban computing system.