$_REQUEST is a bad idea

“Although PHP 5.3 is still in alpha stage and certain features like the PHAR extension or the whole namespace support are still topics of endless discussions it already contains smaller changes that could improve the security of PHP applications a lot.  

Readmore: PHP 5.3 and Delayed Cross Site Request Forgeries/Hijacking

ZEND Framework Links

ZEND Framework architecture

http://phpimpact.wordpress.com/2008/07/28/zend-framework-architecture/

Loading modules

http://phpimpact.wordpress.com/2008/08/12/loading-models-within-modules-in-the-zend-framework/

Controller

http://phpimpact.wordpress.com/2008/09/16/zend-framework-controller-22-drop-in-responsiveness/

Performance

http://phpimpact.wordpress.com/2008/07/06/zend_form-performance-issues/
http://www.phpjack.com/content/zend-framework-performance

IBM articles

http://www.ibm.com/developerworks/opensource/library/os-php-zend1/

click on the show search results link to read more articles

Other links
http://www.cyberlot.net/taxonomy/term/2
http://www.zftutorials.com/
http://www.zendframeworkinaction.com/
http://phpimpact.wordpress.com/2008/10/04/zend-framework-my_view_helper_routeurl/