Today I was playing with v-usb. Of course my stuff did not work as expected. So how to debug USB? A little bit of googling revealed that
sudo modprobe usbmon sudo wireshark &
allows me to spy on the USB bus. Unbelievable. I still have not figured out my issue but I am convinced that from now on it will be much easier.
Do you know other tricks with wireshark besides network monitoring? Wireshark rules :)