The authors employ behavioral theories of human motivation and affect and present an explanation for why some CSCW experience is satisfying and engaging for a user. In a longitudinal experiment, participants were divided into four groups and solved two open-ended problems together using a video-conference system. Traditional metrics of usability and product acceptance were examined with respect to psychological variables such as personality, background knowledge, mindsets (i.e., implicit beliefs) and feelings toward group members. The results show that group-level mutual affect and implicit beliefs on one's ability (e.g., whether intelligence is fixed or malleable) are strong predictors of system usability and acceptability judgments. It is proposed that evaluating one's experience with a CSCW system is a meaning-making process and that the variables that modulate this process also influence subjective judgments of usability and acceptability of a complex collaborative system.