QEMU and USB
Seamless mouse
Starting with version 0.8.1 QEMU can emulate a HID mouse (independent of real used mouse):
qemu ... -usb -usbdevice tablet
For this, the guest OS has to support USB and USB HID devices (e.g. >= Win98 SE).
The big advantage of this is that the mouse can now move seamlessly between host and guest. It isn't "caught" by host or guest, i.e. no Ctrl-Alt to toggle between mouse and keyboard grab any more. This behavior is already known from VMWARE using VMWARE tools.