KenB - 12:50 pm on Feb 12, 2010 (gmt 0)
Another one that can add up to a real time consumption if done hundreds of times is $A=$B[$i][$s]. In my while loops I was putting my array values for loop $i into straight variables to make my code more readable, doing this six times per loop over the course of 160+ loops actually ate up about 4ms more time than just using $B[$i][$s] in my code directly.
The lesson from that one is to watch how you create pointers. They may be fast but even pennies can add up to real money if you have enough of them.