I need to share my experiece with all of you. I design an AC motor controller using 89C2051. Sometimes, my controller miss counting. In my mind I thought that it must be caused by unused pin (floated). So, I design the second prototype. Add an optocoupler as voltage insulator from motor controller and unfloat the unused pins (connected to ground). What did I gain? Nothing! Still my controller misscount, even a better result doesn't comes up.

What do you think guys? From my experience, nothing to be worried about floating or unfloating pins ....

Just sharing mine......