Well, it broke ours, too. Our root site collection was completely inaccessible, and the main SharePoint site was returning an HTTP status code of 500. After 12 solid hours of wild goose chases tracking down erroneous error messages, we installed KB936867. The installation failed on both steps 8 and 9, claiming that it could not start the associated SharePoint services... but upon reboot and manually starting the before-mentioned services ourselves, everything was back to normal.
You can download the savior KB here. I pray that I have saved at least one person the migraines that my department has been going through for the last few days.