I was having wacky mouse action with QEMU and X11, so I did a little research and found the solution. The trick is to use the -usbdevice tablet option when starting QEMU, and to enable the evtouch driver for the X11 server.

Debian makes this super easy! They have xserver-xorg-input-evtouch in unstable, and then you add this to your xorg.conf file and you are good to go:

Section "InputDevice"
  Identifier "Mouse1"
  Driver "evtouch"
  Option "Protocol" "usb"
  Option "Device" "/dev/input/event0"
  Option "DeviceName" "touchscreen"
  Option "SendCoreEvents"
  Option "CorePointer"
  Option "MinX" "0"
  Option "MinY" "0"
  Option "MaxX" "32767"
  Option "MaxY" "32767"
  Option "ReportingMode" "Raw"
EndSection

Thanks to:

http://lists.gnu.org/…/msg00290.html

and

http://qemu-forum.ipi.fi/viewtopic.php?t=2720