In response to this previous post, Ben Ramsey has relayed some of this thoughts on the benchmarks that were done by Jonathan Street comparing functions and their aliases:

Mmy first reaction was something like: "Egads! These benchmarks are stupid and misleading! These functions are simply aliases of each other. There should be no discernible difference, and any buffoon should realize this fallacy!" This was before I clicked through from PHPDeveloper.org to read his post.

After reading his data and going on to the Better Benchmarks post that followed it, he found that most of the results of additional testing came out negligible and that there was almost no difference between the two.

Ben illustrates the proof of this with a few lines pasted from the "ext/standard/basic_functions.c" in PHP's source showing that the code is shared via a PHP_FALIAS function call.