One thing to check if you see glxCreateContext failed when starting Compiz
I post this message partly in case someone else runs into this problem, but also because it will probably happen to me again in 6 months, and I have a short memory for such things. If you use proprietary drivers for your video card, or drivers from any source other than the package manager, and Compiz stops working, try reinstalling the video driver.
I am using the proprietary Nvidia driver for one of my machines. I keep the driver install files around anyway, because I have to reinstall my drivers any time a kernel update comes through from Fedora. When that happens and I don't notice, the next time I reboot my machine, I have no X at all until I reinstall the driver (and all of the modules that get installed with it). It seems there was some other update that overwrote one of the modules besides a general kernel update. If I were wise, I would try to locate the package that overwrote my previous files, but reinstalling works for now.