I believe eZ publish is written assuming that magic_quotes_gpc is off, because it is not ever guaranteed to be there. If it is found to be on, eZ will remove the slashes automatically (see line 124 in lib/ezutils/classes/ezsys.php if you're interested). This will cause a performance hit. Magic quotes is generally seen to be a bad idea, in fact it will be removed along with safe mode in PHP6: http://www.corephp.co.uk/archives/19-Prepare-for-PHP-6.html
