If your plastic unibody Macbook is having peeling rubber butt issues, you aren't alone. Apple's now actually fixing the problem for free - either through the Genius bar or a DIY kit. They'll even refund any money you've spent before.
Apple has determined that under certain circumstances the rubber surface on some MacBooks may separate from the bottom case of the system. MacBooks shipped between October 2009 and April 2011 may experience this issue. Apple will replace the bottom case of any affected MacBook, free of charge, that exhibits the issue.