The problem, according to Cupertino’s engineers, is that “under certain circumstances, the rubber surface on some MacBooks may separate from the bottom of the system“. The MacBook Bottom Case Replacement Program has been set up to take care of customers who have fallen victim to this problem.
MacBooks that have shipped between October 2009 and April 2011 are covered. This is another way of saying “all white unibodies” as Apple didn’t start shipping laptops with a white rubber bottom until the release of the white plastic unibody on October 20, 2009. MacBook Pros are not part of this program, as they have a different bottom.
A replacement can be ordered online, or can be obtained by setting up an appointment with a Genius at an Apple retail store. If you choose the do-it-yourself option you’ll receive not only a replacement bottom cover, but also a screwdriver sized to fit the screws on the bottom of your Mac and a full set of new replacement screws. Instructions are included.
If you already had this problem and were forced to pay for a replacement, Apple can issue a refund.
Source: Ars Technica