PHP twice as fast? Has anyone used this, yet?

[Firefox Wins]

This is a PHP compiler that gives over 2x speed improvements...

Anyone here heard of 'HPHP' / or used it yet?

• 2x faster, really?
  

Edit: FYI:
The fact there are so many PHP compilers illustrates a point – the mainstream PHP implementation (Zend) is inherently a sub-optimal design. It isn't multi-threaded, which means it relies on multiple processes to dispatch requests – which means a lot more memory and process juggling than you'd ideally have...
~same source