For the majority usb 3.0 is backwards compatible with usb 2.0. But there is an exception I do not quite understand. I am referring to this page:
http://www.datapro.net/techinfo/usb_3_explained.html#USB_Backwards_Compatibility
It says a USB B male connector is not compatible with a USB 2.0 B female jack. I can't seem to find a photo of a USB 2.0 B female jack but what devices use a USB 2.0 B female jack?