A major rationale for keeping the space shuttle flying this long was to complete ISS so that it could accomodate a crew of six. Six could do more science than three. Fine. Through most of December, 2009, however, the ISS crew will have a grand total of two.
Most of the time of the two men will be devoted to station keeping duties. Some science will be done, but the emphasis will be on keeping the station functioning.
A Soyuz flight is scheduled for December 23 that will bring the ISS crew strength back up,