Information structure important for information reuse
John Udell's discussion of Apple's Knowledge Navigator is a wonderful overview of a Personal Information Cloud. If the tools was more mobile or was shown synching with a similar mobile device to have the "knowledge" with the user at all time it is would be a perfect representation.
Information in a Personal Information Cloud is not only what the user wants to have stored for retrieval when it is needed (role-based information and contextual) but portable and always accessible. Having tools that allow the user to capture, categorize, and have attracted to the user so it is always with them is only one part of the equation. The other component is having information that is capable of being captured and reused. Standards structures for information, like (X)HTML and XML are the beginnings of reusable information. These structures must be open to ensure ease of access and reuse in proper context. Information stored in graphics, proprietary software, and proprietary file formats greatly hinders the initial usefulness of the information as it can be in accessible, but it even more greatly hinders the information's reuse.
These principle are not only part of the Personal Information Cloud along with the Model of Attraction, but also contextual design, information architecture, information design, and application development.