OCLC's web based interface to WorldCat, WorldCat.org, is becoming an interesting resource. I think it is a tool that catalogers and metadata librarians can use in creative ways. For example, one of the catalogers I work with searches for serials records in WorldCat.org before using Connexion. He likes the clean, simple interface and the fact that you can see other libraries' serials holdings. Another cataloger I work with suggested looking for call numbers from other libraries when the master record in WorldCat is missing one. Because it links to member libraries' online catalogs it's a good way to find bibliographic data beyond the master record. Recently, I found a record missing the call number and LC subject headings completed in a library's local catalog. WorldCat.org would be an even better cataloging tool if it had a MARC display. So try adding it to your list of web based cataloging applications.
UPDATE: Someone from OCLC was kind enough to clue me in to the fact that WorldCat.org is directly accessible through Connexion. They added this functionality last year. When a record is displayed in Connexion, go to the View menu and choose "Find in a Library." WorldCat.org will open in your default browser to that record. Very cool!