I disagree fundamentally with the idea of booing purely on the basis of ineptitude. Let's face it, we all have good days and bad days. Just imagine for a second how you'd feel if you got half as much stick as footballers do everytime you had a bad day at the office?
What really rankles with me is when players show a lack of effort or desire, or a downright shoddy attitude. In that instance, and only in that instance can I understand why people might boo.
I have to say, I still think it's counter-productive though. I find it hard to believe that the likes of KMB or Reuben Reid were ever inspired to work harder for the team as a result of the fans getting on their back.