HipHop engineer, here. Unless you consider programming in C++ to be [implicitly] programming in machine language, this doesn't make a lot of sense. Our application engineers write real, no-fooling PHP, at exactly the same level of abstraction as they always have. They usually don't bother compiling it either, instead iterating using our interpreter which behaves more like a drop-in replacement for Apache+Zend.
I've been looking at HipHop lately -- can you give me a general idea of how much you have to work around HipHop for it to still compile? I know that the references I've seen to it have all indicated that it might choke on certain types of code, but I'm curious as to how mindful you have to be?
If you stick to the brightly lit parts of the language, things will work. The Facebook codebase was and is enormous, so the vast majority of PHP has to work as advertised. The one big thing that's ruled out is eval, but other wacky PHP tricks ($f(), $C::staticMethod, $obj->$methodName(), foreach order, etc.) work. Outside of eval, you have to go out of your way to break it.
That said, it's a young project, and things can be a bit rocky. Including compilation in your deployment process is also a pain; do not kid yourself about that. It's kind of "industrial strength" in general; unless you care about how many PHP requests you can squeeze out of a unit of hardware, HipHop doesn't have much to offer.
