SpaceX announced that it will slip the launch of the Dragon spacecraft aboard a Falcon 9 from the original 7 February 2012 date. The specific reason for the delay was not specified, but was related to a “sense of responsibility in returning US crewed access to LEO”.
NASASpaceFlight notes that SpaceX was slipping in order to allow for due diligence “safety checks” ahead of launch.
It is expected that the slip will only be two to three weeks.
Updated 20 January:
If the delay is longer, then the ISS crew will be reduced to three (3) when Soyuz TMA-22 undocks on 16 March. Two astronauts are required to grapple and dock Dragon. TMA-04M is scheduled to arrive on 1 April, restoring the ISS crew to six (6). Most of April is clear of activity, assuming SpaceX can be ready by then.