The HipHop VM blog has a new post today with some updates around the compatibility work they're doing getting popular PHP projects to work 100% on the platform (and have all unit tests pass).
Earlier this year we set an ambitious goal of passing the PHPUnit test suites of 20 popular frameworks by the end of June; at the time, we were passing on only 6! With a huge amount of help from the community (especially our OpenAcademy students), we’re proud to have hit this goal more than 2 months early, and we have more frameworks expected to reach 100% shortly.
Included in their list of projects/frameworks are things like Assetic, Composer, Doctrine2, Guzzle (v3), Laravel, Mockery and Monolog. Now that they've made significant strides to get the HHVM up to a greater level of compatibility, they're going to focus in on the issues list from GitHub to resolve problems there.