I would view this question similar to being asked about an identified weakness (or developmental need, as we call it in our performance evaluation). I have answered this question before with a "messy desk" which I have come a long way now after having taken diligent steps to manage the desk clutter way better than what it used to be before. This approach has met with mixed results. Most technical interviewers (I am an accountant) have identified this as part of their weakness too. But, HR has been more concerned about this answer leading them to believe that it is a signal for un-cordinated, indisciplined work habits. I look forward to reading some better answers on this one.