Upgraded to 3.5, and could no longer see content in the Edit Pages box. Problem occurred identically in Safari, Internet Explorer, Firefox, and Chrome.
Inserting define('SCRIPT_DEBUG', true); in the wp-config.php and this corrected the issue.
Below is the output from the error console in firefox.
Error: ReferenceError: getUserSetting is not defined
Source File: http://computerpi.com/wp-includes/js/tinymce/plugins/wordpress/editor_plugin.js?ver=358-23156
Clearly I am not the only one that has had this issue. Will now reinsert the SCRIPT_DEBUG line and use until the bug is fixed.