This paper argues for evaluating the impact of persuasive systems on users beyond metrics that focus on system usage, based on an interview study of 16 Wii Fit users. While exploring their experiences and reasons for abandoning the system, two main themes emerged: the tension between Wii Fit as a fitness tool and a game, and ways participants reacted to the system’s feedback about their weight and performance. Some participants used Wii Fit as a ‘gateway fitness’ tool, moving beyond it to other fitness routines. Additionally, some users had significant emotional reactions to the Wii Fit’s feedback. We argue that these ‘side effects’ are crucial considerations for the design and long-term evaluation of persuasive technologies. Author Keywords Wii Fit, e-health interventions, persuasive technologies. ACM Classification Keywords H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous. General Terms Experimentation.