The USPTO will be closed Friday, December 26, 2014. Any action or fee due on Friday, December 26, 2014, would be considered timely if filed on the next succeeding business day, specifically, Monday, December 29, 2014. You can see this on the USPTO web site here and here.
A big thank you goes to Bryan Wheelock and Matthew Hintz who provided the citations to the items on the USPTO web site.
Yet another nice person (Scott Barrett) points out that apparently this closure was announced by the White House on December 5, 2014.