If you've tried out the latest Zend tool, Zend Studio 3.0, you've seen their "profiler" tool. Using this tool, you can profile your scripts and see which are taking the longest, etc. Well, thanks to LinuxJournal, you might not need to purchase that IDE at all.

In PHP Performance Profiling, they state: Due to the incredible growth of PHP in the last couple of years, it's now being used for tasks ranging from tiny scripts to large-scale Web applications. [...] The answer is a technique known as performance profiling. Performance profiling runs your code in a controlled environment and returns a report listing such statistics as time spent within each function, how long each database query takes and how much memory has been used.

They use projects like the PEAR Benchmark class, XDebug, and the Advanced PHP Debugger to show some stats on your scripts. APD even includes a script called "pprofp" that creates a top-like detail view of which calls in your script take the longest. Cool stuff...