I don;t think you get any notification unless a USB device is attached, I will check that tomorrow with my S3. Additionally, I don;t think the S3 can supply enough power for a USB device of more than 32 GB the power to the USB port is very limited on phones, about 100 ma vs. 500 ma for a standard PC USB port. You can check whats going on by looking at a LOGCAT on terminal if you are using a rooted ROM. This article / video may also be helpful.
http://www.androidnz.net/2012/06/samsung-galaxy-s-iii-connectivity-demo.html?m=1