The "Insert into Post" button in the media uploader is not working for me after the 3.5 upgrade.
I've deactivated all of my plugins and it still doesn't work.
I looked through all the threads about this and tried adding
define('CONCATENATE_SCRIPTS', false );
to my wp-config file and it still doesn't work.
The only thing that did work was switching to Twentytwelve.
The theme I am using is a customized version of Underscores.