In May 2011, Apple started a program to replace the bottom case of white MacBooks, as, under certain conditions, the rubber layer could come off the bottom of the notebook.
Few days ago, as noted by the MacRumors, Apple quietly extended the duration of the program by two years.
Here is the modified part (with emphasis):
This program covers MacBooks affected by the problem for four years from the original purchase date. Apple continually evaluates technical support data and extends this program as needed.
Until last week, the program page still quoted "for two years".
As the program covers MacBooks sold between October 2009 and April 2011, this means that even the very first machines sold are still eligible for replacement until October this year. Not bad.