Mouse Cursor Alignment with KVM/QEMU and VNC

After getting repeatedly annoyed with the fact that the mouse pointer in vncviewer on virtual machines never properly follows the local mouse pointer, and is always offset, I spent far too long trying to find a solution. The answer is actually quite easy:

libvirt guest XML:

  
<devices>
<input type='tablet' bus='usb'/>
...
</devices>

Command-line:

  
qemu -usbdevice tablet