I've used Sass, Less and a number of other approaches to this general area (of "enhancing" our CSS authoring experience) and whilst nice, have yet to really be convinced by the whole idea. If the tools are there and you find them useful, great but I'm happy (relatively) with POCSS (Plain Old…).

santa, as .Nick mentioned, it's written in Ruby but that's no reason at all not to make use of it in your PHP development environment (unless you're embedding PHP into your CSS files).