in reply to
Optimizing existing Perl code (in practise)
The real trick isn't optimizing your code but optimizing your solution. Maybe you can write the same code three different ways but if that code implements an O(N2) algorithm when there is an O(N) algorithm that will do it doesn't matter much whether you shave a few microseconds off each iteration.
Successfully choosing the right algorithm takes careful consideration of the problem. If there is a secret to it at all it's probably choosing the right representation for your data. How to do that is a matter of experience and education. There isn't a cookbook solution to it because it usually depends greatly upon details of the problem you need to solve.
"My two cents aren't worth a dime.";