The usage of Service Layer with a data mapper, how is this necessary?

Well sorry for bumping this thread, I have an additional question about a service layer in a complex web application. I mean, should the service layer be domain-oriented or application-oriented. By domain-oriented I mean one service object per domain object/mapper object, and application-oriented implies one service object per controller object.

One example I can think of is a CMS with a user system, in which the user can register, authentificate(login/logout), manage account and view profile. The domain model is User class, with UserMapper as its corresponding data mapper. The app controllers are register, auth, account and profile, which may have actions and params. In this case, would it make sense to define a UserService parallel to the User/UserMapper domain, or to define services like RegisterService, AuthService, AccountService and ProfileService associated with these app controllers? I know this can get confusing, service layer after all is an intermediary between Domain(model) and Application(controller) layer/logic.