PHP is a wonderfully flexible and powerful language, but it's notorious for having a very polluted global namespace and no way to define separate namespaces other than wrapping things in classes. Users have been begging for a better solution for years, but to no avail. It looks like that may finally change, though.
The release of PHP 5.1.0 just before Thanksgiving introduced a new native Date class for (not surprisingly) manipulating dates and times. Unfortunately, PHP's developers either didn't notice or didn't care that there was already a very popular PEAR class called Date. So anyone who was using the PEAR Date class and upgraded to PHP 5.1.0 suddenly found themselves using an entirely different and incompatible native Date class, which broke hundreds, if not thousands, of applications.
The PHP mailing lists were instantly abuzz with users complaining about the breakage and developers proposing half-baked ideas for solving the problem by — at long last — introducing namespaces. Thankfully, cooler heads realized that namespaces are a big change and the most important thing was to fix the immediate problem, so PHP 5.1.1 was quickly released minus the new Date class.
This incident seems to have hammered home to the PHP team just how important namespaces are and how painful it is to try and design a language as big as PHP without them. Maybe after this they'll finally get their shit together and add namespaces in PHP 6.