This report addresses the objectives of a national survey of users and non-users of online catalogs (OPAC's) as they apply to MELVYL and its implementation in the University of California (UC) Libraries on nine campuses. These objectives were to collect information to enable libraries to improve implementation of support services for public access online catalogs, remove barriers to OPAC use and extend service to potential users, and to assist designers to improve system interface features. Data sources for the Public Access Project as a whole are described, though this report focuses on findings from the analysis of user questionnaires from University of California respondents and selected data from the MELVYL transaction logging subsystem. Additional sections discuss the two cycles of data collection, development and revision of the data collection process and instruments, questionnaire administration and specific sources of UC data, the use and evaluation of the online catalog, its features, and the library environment. This report results from one of five investigations of user and non-user responses to public online catalogs which used a jointly-developed survey in all the participating libraries to identify the problems experienced by catalog users and their preferences for improving the catalog, as well as barriers to catalog use for non-users. (LMM)