Forget what I said about the default behavior having changed. This machine is a can full of Heisenbugs! After the fifth reboot, kms came back with a vengeance. Currently not even the conf file won't stop it. The only way I have to use the machine is the kernel from Ubuntu 10.4 that I hand-copied onto it. Apparently they have kms disabled for the i915 by some brute force method. The dmesg output contains the line
/i915/ disabling kernel modesetting for known /bad device/.