GPO for blocking USB drives and media devices

I've got a GPO for blocking this. However, it is not effective. I've attached the settings summary from Group Policy Management. I'm pretty sure it's airtight. I've even got some settings in there to lock down Windows Media Player for those few clients that are using Windows Vista so that the users can't use WMP's MTP protocols. Am I missing something? The only oddity I can think of off the top of my head is that the head guys wanted this applied to PCs rather than users or groups.