Will Web 2.0 ever meet library catalogs? The Web is changing: we can define it "web 2.0" or "Social web" or we can use some other word, but certainly we can't deny that there is a change. Some elements, above all those due to the on-line availability of content (i.e. full text) and that some contents (users generated contents) are produced by users, now called "prosumer", are also generating change in the interfaces of libraries' catalogues on the web: the web OPAC. This address will pinpoint some particular changes in interfaces, in information retrieval systems and also how catalogue content is shown. The intention is to assess whether and to what extent these elements could be applied to the library catalogue.