Using: xorg-x11-server-Xorg-1.7.1-7.fc12.x86_64 kmod-nvidia-190.42-1.fc12.4.x86_64 (rpmforge) Opening the start-menu, krunner (through Alt-F2) or the like results in 10-20sec delay before the expected window opens. In http://bugs.archlinux.org/task/17037 it's suggests that it might a problem related to the RedHat-patch xserver-1.7.1-window-pictures.patch (removing it seems to resolve from the problem for some folks).
*** This bug has been marked as a duplicate of bug 533620 ***
As mentioned in that bug I gave the quickfix from Rex Dieter a try. Installing his xorg-packages (with the removed redhat-patch) worked: http://rdieter.fedorapeople.org/repo/ For further information please see above mentioned bug.