Personalization was a hype in the late 1990s. Several organizations offered (and are still offering) personalization services for their customers. From e-commerce applications we know that people are willing to provide their names and other personal data if they know exactly how this information is used. Many of us are using different Digital Libraries on a regular basis. If our interests change, we have to update all profiles stored at these different server systems. This task is time consuming and error prone. Since there is no single Digital Library which covers all information-resources a user needs, there is a need to exchange personal data (especially personal interests). In this article we will show that user-profiles are important to satisfy users’ needs, which information about users should be stored in profiles. Just parts of the profile must be shared with other service providers. It will be shown, that it is not possible to predict usage of properties. Therefore the user itself must decide which properties may be shared with others and which properties should not be accessible by certain services.