1. A method of document-based processing, comprising: inputting a document; extracting features from the document; querying an index using at least a subset of the extracted features and, in response, receiving identifications for selected document classifiers from a larger pool of document classifiers; processing the document using individual ones of the selected document classifiers, thereby generating corresponding classifier outputs; and based on the classifier outputs, at least one of (1) categorizing the document within a computer database and (2) providing feedback information to a user.