On the NetTuts.com site today they've posted a new tutorial showing you how you can use WordPress with HHVM now that they're 100% compatible.

Over the past few months HHVM has taken the PHP community by storm. Since WordPress 3.9 was released, HHVM is now 100% compatible with WordPress.

Unfortunately, HHVM is not quite ready for use in production in self-hosted environments. In my experience, HHVM crashes about once per day, which makes it not viable for a site where high availability is important. Recently, WP Engine has released project Mercury which seamlessly allows HHVM to gracefully fail by falling back to PHP 5.5 when it fails. In this article, we're going to install HHVM on an Ubuntu server running the latest LTS release, 14.04.

They walk you through the full process including:

• installing MySQL
• Installing Nginx
• Installing HHVM
• Setting up and configuring them all to play nicely with WordPress

It's a pretty short article and doesn't get into the specifics of the WordPress setup steps past ensuring it's working with HHVM but it does give a good starting place.