Although Drupal 7+ runs smoothly on PHP 5.3, Drupal 6 still feels much better with PHP 5.2. Therefore developing for both D7 and D6 at the same time becomes much less painful when running both versions of PHP in parallel. How this can be achieved on Ubuntu 12.04?
Few interesting thoughts about writing easy-to-read PHP code.
Well, maybe this is not really about hidden features of PHP, more about why PHP is so great (and easy) language to program with, including lots of interesting tips and tricks.