I packed in simply because I just couldn't face doing even one more, but that's after several hundred I would think. I did actually go full time for about 3 years. The last three I did on consecutive Saturdays were all in the pouring rain with nightmare venues for taking ALL the shots indoors. That just about made my mind up. I don't have to do it any more so I don't.
As Steve said you need two of everything - belt and braces, sooner or later you'll come unstuck if you don't.