PHP5 Speed Issues

Hi Fellows, I figured out, that PHP5 runs faster when I am not inherit classes, I hope I use the right word. I mean the class sub_class extends main_class notation. As well I figured out, that I in most cases should references in foreach loops. like foreach($array as $key => &$value) { } Lots of memory is saved by that. Now I would like to know, what other speed improvements might be possible. What about autoload of classes, will it improve speed when I throw the code out? Are there other things I should take care of. I would like to know as much as possible. Please go deep into your- self and tell me every little thing on how you improved your applica- tions for speed and memory optimisation, to make this thread the best compendium on performance and memory optimisation. Thank you very much, fellows and a merry merry christmas! Sascha