The 2 updates of kdelibs today don't work with compositing.
This morning I updated and when I rebooted later on in the day, my desktop
froze up and not even keyboard responses worked. I had no option but to alt-
sysrq.
Then I booted again and updated and got a second kdelibs today, namely
kdelibs-4.6.4-5.fc15.x86_64. Again, the same problem (after reboot). Desktop
frozen, no recourse but alt-sysrq.
I booted into multi-user.target and manually edited kwinrc to disable
compositing. Again I rebooted, and now I have a working desktop, but without
desktop effects.