I've been spending some hours trying to get HipHop PHP working on my Ubuntu 12.04 install. After three failed attempts, this got me there (on a fresh Amazon instance):
sudo vi /etc/apt/sources.list
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install hiphop-php
I was then able to run commands like hhvm sample.php params-1 params-2, but oddly enough, scripts were taking longer.
The documentation online for this project seems scattered, often times with pages 404-ing. I kept seeing references to both hhvm and hphp, however got confused as the install didn't seem to give me access to hphp.
Well, it was renamed to hhvm-analyze. This is the library I wanted to use to test some pretty hectic code. I'll follow up with the results of this test when I can.