My girlfriend's machine has been rendered completely unusable by this update. She downloaded it fine and installed it, then a dialogue box appeared informing that the update had been deleted and that it should be installed again. (Safari was open during the installation.) She thinks she tried to click 'OK' and after that her computer froze and she forced it to shut down. Since then when we try to start it up it hangs on the spinning icon. I'm thinking the best solution would be to startup in FireWire Target Disk mode, copy all of her files and settings across and reinstall OS X. Thoughts?