I applied patch 6788 and it pretty much broke our entire website.
CMS Static blocks randomly stopped showing up, for example:
$str = Mage::app()->getLayout()->createBlock('cms/block')->setBlockId('prs_footer_contact')->toHtml();
var_dump($str);
returns
string(0) ""
It was not possible to create or edit CMS static blocks, the admin website was entirely broken by "Invalid Form Key" - account creation was broken because Mage_Core_Controller_Varien_Action::_validateFormKey always would return false, despite it appeared the account creation page had been updated to include the hidden form_key form variable.
This was a complete mess, I eventually just un-applied the patch because it's not worth playing a game of whack-a-mole to fix all of the bugs this patch created.
