As unique as each person is, so is each personal library. People organize information they need on a daily basis in what could be called a "personal library". Studies about personal search engines showed, that such a personal library is not only for storing, but also for organizing your daily work. If your library is well structured, you get an overview on your projects and current tasks. This is why structure is needed to organize the collected information, and a search engine to dig through a pile is not enough.