The large-scale adoption of computer mediated communication technologies has resulted in what has been described as "mass interaction": shared discourse between hundreds, thousands or more individuals. A number of theoretical papers have made the argument that because of the existence of various technological and psychological constraints, the forms that mass interaction takes, can be understood partly in terms of system dynamics. In particular, it has been suggested that user information overload results in nonlinear feedback loops which impacts on discourse structure. This paper describes an empirical examination of three hypothesized effects of such loops by the analysis of 2.65 million USENET messages posted to 600 newsgroups over a 6-month period. Statistical analysis of the data demonstrated the existence of the hypothesized effects and support the assertion that individual 'information overload' coping strategies have an observable impact on mass interaction discourse dynamics. This in turn suggests that the usability of computer mediated communication technologies can be examined in terms of group-level usability.