The latest versions of virt-manager don’t release the mouse pointer when you’re doing X forwarding to a machine running OS X. This can lead to a rather frustrating user experience since your mouse pointer is totally stuck in the window. Although this didn’t affect me with CentOS 6 hosts, Fedora 18 hosts were a problem.
There’s a relatively elegant fix from btm.geek that solved it for me. On your Mac, exit X11/Xquartz and create an
~/.Xmodmap file containing this:
keycode 66 = Alt_L
keycode 69 = Alt_R
add Mod1 = Alt_L
add Mod1 = Alt_R
Start X11/Xquartz once more and virt-manager should release your mouse pointer if you hold the left control key and left option at the same time.