Computer systems and methods allow users to annotate content items found in a corpus such as the World Wide Web. Annotations, which can include any descriptive and/or evaluative metadata related to a document, are collected from a user and stored in association with that user. Users are able to annotate and view their annotations for any document they encounter while interacting with the corpus, including hits returned in a search of the corpus. Users are also able to search their annotations or to limit searches to documents they have annotated. Metadata from annotations can also be aggregated across users and aggregated metadata applied in generating search results.