The news in the PHP world today is Facebook\'s HipHop, which:
HipHop for PHP isn\'t technically a compiler itself. Rather it is a source code transformer.
Well it "transforms" PHP into C++ to help performance of a largely scalable website.
So, HipHop is for when you have a website that you started at Harvard that you quickly grow into a billion dollar company and that people are making a movie about starring Justin Timberlake. When you have such a website and want to save CPU cycles, but don't want to rewrite your codebase, you use HipHop.
If you are just starting out, unless you are trapped on a desert island with only PHP programmers that refuse to learn a more scalable language, you don't use HipHop.