HHVM is a very interesting project since it's all open-source and it is indeed extremely fast and what powers all of the PHP code at Facebook. HHVM has only been getting faster and in many workloads is a great deal faster than the official PHP interpreter itself, but Facebook wants better.
For this three-week lockdown through November the team is focusing on nothing but performance and parity work. The developers are keeping track in real-time of their progress on the performance front (web-page serving, % cputime win, and % instructions) along with parity in terms of running a number of unit tests on a number of PHP projects outside of Facebook like Drupal, phpMyAdmin, phpBB3, MediaWiki, and Joomla.
More details on Facebook's HHVM performance/parity push can be found via the HVVM blog post. This latest push comes just a few weeks after the release of HHVM 2.2. The HHVM 2.2.0 release features support for reading PHAR files, Redis support, php.ini support, Jemalloc is now the default memory allocator, and there's a number of other changes and fixes throughout; HHVM 2.2 details are available via this post.