The Web-based negotiation support system (NSS) Inspire has been used in experimental negotiations by over 2,000 students and professionals worldwide. Feedback from a survey conducted among the users shows that more than 80% would use a NSS similar to Inspire to prepare and practice negotiations and 61% would use such a system to conduct actual negotiations. In this article we present an assessment model for Internet-based systems (AMIS) to analyze factors that led to this attitude. The empirical results indicate that the intention to use a system in the future is strongly influenced by the users' assessment of the system. Furthermore, users differentiate between various components of a NSS, and analytical features are evaluated differently from communication features. In addition, actual outcomes of negotiations and the users' experience as well as national culture strongly influence system assessment. We conclude that (a) there is generally a relatively positive attitude towards new technologies such as Web-based NSS, (b) that user characteristics need to be considered to develop effective negotiation support, and (c) that acceptance of different features of a system can vary to a considerable extent for users having a different background.