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