So far, conceptual modeling of Web applications has been used primarily in the upper part of the life cycle, as a driver for system analysis. Little attention has been put on exploiting the conceptual models developed during analysis for application evaluation, maintenance and evolution. This paper illustrates an approach for integrating the use of conceptual models in the lower part of the application life cycle, by exploiting them in quality analysis and usage evaluation. A prototype tool for supporting the described evaluation activities is also presented.