Installing Omeka 0.9.0 a small Gentoo test server we did encounter the whitescreen mentioned in the troubleshooting section, but the error wasn't caused by the AllowOverides All directive. Our PHP installation, version 5.2.5, was not compiled with the mysqli extensions which caused the blank page. It took me a little to trace the cause down to the failing Db.php class. A quick recompile fixed our problems and the rest installed cleanly, but do you think it would be possible/useful for Omeka to check for this in the future? Or at least print something useful if you are missing a function?
A simple
if (!function_exists('mysqli_connect')) {
throw new Zend_Config_Exception('PHP missing required MySQL improved extensions.');
}
would have made the debugging a little easier.
And thanks to MrDys for this thread about the RewriteBase information.