People seem to want to know if HPHP is widely useful outside of Facebook, and some people are saying “no”. I disagree strongly. In order for HPHP to be useful, you need to have a PHP application which is suffering due to PHP interpreter performance. That matches Facebook perfectly, and they’ve always been the canonical example I use to explain why PHP compilers are interesting. But you don’t have to be Facebook size or scale to have performance problems.
via A rant about PHP compilers in general and HipHop in particular..