Very nice idea, this might prove very useful for privacy concerns. However I think you should spend a little time making it work under PHP strict standards (ie errors at E_ALL|E_STRICT).
Right now the script throws notices and warnings every now and then.
Also you should not use short tags (<?php is better), and closing tags (?>) in your classes files are useless.
All in all a nice one, just needs a little more effort to make it really good :-)