25. The system as recited in claim 21 , wherein the first portion of text is identified from annotation information received from a plurality of electronic devices.
21. A system comprising: one or more processors; one or more computer-readable media; and one or more modules maintained on the one or more computer-readable media that, when executed by the one or more processors, cause the one or more processors to perform operations including: accessing training data, the training data comprising one or more features of a first portion of text from within a first body of text, the first portion of text having been selected through a first user interaction received by a first computing device associated with a first user; training a classifier based at least in part on the accessed training data, wherein, once trained, the classifier is configured to assign scores indicating a probability that a corresponding portion of a second body of text will be annotated by a second user based on the first portion of text having been selected through the first user interaction; identifying a third portion of text and a fourth portion of text from within the second body of text; using the classifier to assign to the third portion of text a first score that indicates a probability that the third portion of text portion will be annotated by future users; using the classifier to assign to the fourth portion of text a second score that indicates a probability that the fourth portion of text portion will be annotated by future users, wherein the first score and the second score are assigned by the classifier based at least in part on the first user interaction; ranking the third portion of text and the fourth portion of text based at least in part on the first score and the second score; and identify the fourth portion of text, the fourth portion of text being identified based at least partly on the ranking.