You need to file a bug on the package. It shouldn't be sitting in I/O wait states or other things when you click logout.
An update on this: it is xorg-x11-drv-synaptics causing the bother.
To verify this, you can build a live cd from the F11 release repo, without enabling updates. Put it on a USB stick, boot off it, and you can log in and out with no trouble. Then
yum update xorg-x11-drv-synaptics