1. A method of indexing documents, the method comprising: extracting feature information from each of a plurality of documents to be indexed; defining a plurality of indexes based on statistical properties of the extracted feature information; for each of at least some of the documents: selecting one of the indexes as a destination index for the document based on the feature information extracted from the document; and adding a searchable representation of the document to the destination index; and storing the plurality of indexes in a computer-readable storage medium.