Seems like a security flaw. Anyone can pick up my phone, plug it into a USB port and copy files within seconds. Normally, you'd have to at least have to reboot into recovery, which requires a forced reboot and knowing the proper keys to do that and to enter recovery. As it stands now, even a child could plug in my phone and access the entire SD card.
It's also annoying that if I plug in the phone to my PC to charge while I'm listening to music on it, I don't get the lock screen where I have music controls. I instead get the USB mounting screen. I just have to press the Home key to show the lock screen, but it's been bugging me.
Is there any way to disable this? It wasn't this way in CM 10.1.