Yesterday Facebook launched HipHop, a converter from php to c++ so your apps can run twice as fast due to them being compiled not interpreted.
Today I’m excited to share the project a small team of amazing people and I have been working on for the past two years; HipHop for PHP. With HipHop we’ve reduced the CPU usage on our Web servers on average by about fifty percent, depending on the page. Less CPU means fewer servers, which means less overhead. This project has had a tremendous impact on Facebook. We feel the Web at large can benefit from HipHop, so we are releasing it as open source this evening in hope that it brings a new focus toward scaling large complex websites with PHP. While HipHop has shown us incredible results, it’s certainly not complete and you should be comfortable with beta software before trying it out. – Haiping Zhao (Facebook)
HipHop is for scaling large multiserver high traffic sites like Facebook. In your regular application, you will get no great advantage from it. It is definately something to be aware of but it does make you think if your trying to compile PHP using a tool like this why not develop in C# (ASP.NET MVC 2 maybe?) that is compiled anyway?