Whatever you do never give them your worst weakness (or even your worst three), interviewers never expect you to give the worst trait/ weakness so they will always imagine something worse and if you already gave them something quite bad well then it is downhill from there.
Always turn your faults into positives like mentioned already. Stubborn equals never giving up on a problem.
But above all this is partly a trick question, like when they used to ask is Jaffa Cake a cake or a biscuit, do you watch Coronation Street or Eastenders. Sure they are interested in the answer and to see how you turn a weakness into a strength, but the important bit is that you don't freeze up and panic.
Don't worry and good luck.
Edited: 01/08/2011 at 01:00