pyusb

Why does PyUSB / libusb require root (sudo) permissions on Linux?

I have been toying around with PyUSB lately, and found that it works beautifully on Linux (Ubuntu has libusb 0.1 and 1.0, as well as OpenUSB)... but only if I run the program with root privileges (with sudo, of course). Can anyone tell me why it requires elevated privileges and, more importantly, if I can change the permissions somehow ...