This is an updated version of Trashie's dotProject permissions handling performance fix. I have merged the required functionality into the 2.1.2 release of premissions.class.php as there were some compatibility issues when migrating from 2.1.1 to 2.1.2.
To install just exract the two files from the zip into you /dotproject folder. execute the initDotpermissions.php (as this will create a quick reference table for the permissions rules. Then move the permissions.class.php to your /dotproject/classes folder (backup the existing permissions.class.php first just to be on the safe side) and you are set.
More details about this performance fix including features and limitations can be found in Trashie's original thread in dotproject forums: