1. A computer-implemented method comprising: accepting, by at least one computer, input specifying at least one track; selecting, by the at least one computer, a set of play logs from a corpus of play logs, each play log in the corpus corresponding to a user and being used to identify track occurrences from observed behavior of the user, each play log in the set is selected by taking into account a number of occurrences of the at least one track in the play log; and selecting, by the at least one computer, a set of tracks for a playlist from a corpus of tracks comprising tracks found in the set of play logs selected, wherein selecting the set of tracks comprises analyzing track occurrences identified from observed behavior indicated in each play log in the selected set and track occurrences identified from observed behavior indicated in the corpus of play logs, each track in the selected set of tracks is determined to be overrepresented in the selected set of play logs based on a significance measurement for the track that takes into account multiple occurrences of the track in a play log.