UI Garden: "During the doctoral research, Ruth Mugge investigated the topic of product attachment – the strength of the emotional bond a consumer experiences to a specific product. [...] Based on the literature, four factors were distinguished that can influence product attachment: self-expression (can I distinguish myself from others with the product?), group affiliation (does ownership of the product connect me to a group?), memories (related to the product) and pleasure (provided by the product). Although these factors are all relevant for stimulating the experience of attachment to products, they differ in the degree to which designers can influence them through product design."
Emotional Design: Why We Love (or Hate) Everyday Things, Donald A. Norman.