Sounds exciting:
Yii is not compatible since uses eval().
Rarely used 
I’m aware of Yii using eval() for RBAC. Does it use eval() in other places too? Could it be an option to change checkAccess() so that it uses function callbacks, for example? (Or PHP 5.3’s anonymous functions, for that matter)
The developer docs and wiki don’t seem to be online yet, so maybe we should wait until a more exhaustive list of unsupported functionalities is released. If other dynamic functionalities like autoloading or magic functions aren’t supported, the changes required for Yii to support HipHop may be too great…
Here is conference: http://www.ustream.tv/recorded/4409735
In the video you see they also have problems with function_exists() calls.
Sourcecode not yet released as far as I can tell.
Github repository is now made public - still, the source-code is not released yet but there are some useful informations.
Has anyone looked in to this recently? I’m about to give it a whirl.
maybe you can try Roadmap as it seems to have less drawbacks