On the Facebook Engineering blog there's a new post summarizing the last six months since they released the HipHop tool for PHP along with some of the stats from the time.

Since February, the team has made HipHop another 1.8 times faster and all of that code is open source. We’ve also seen improvements to PHP itself with the additions to PHP's trunk in April being about 10% faster than 5.3.

They talk about projects they've worked with (including Drupal and WordPress), community contributions, a first use of it in production at ocProducts and the work that's been done for FreeBSD.