I just updated an Ubuntu Oneiric to Raring and the VM that works fine on one
fails to start a VM with this passthrough:
<hostdev mode='subsystem' type='usb' managed='no'>
<source>
<vendor id='0x055f'/>
<product id='0x040b'/>
<address bus='3' device='8'/>
</source>
</hostdev>
It just dies at boot time.