No 3d sessions with nouveau & 3.7.0-2 on some? chipsets

[mc4man]

At least seen here with a 8400m (Dell
Symptoms pretty straightforward -
boots fine to greeter then nothing but a Desktop image & cursor, both on unity & GS.
Nothing is possible once leaving the greeter.
Same on current live image > 'Try Me'

Works fine with Classic (No Effects) & nvidia-* drivers
Seen with both rc5 & 6
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1080389

[mc4man]

Fixed here with linux-* (3.7.0-4.12), should make it into daily image in a day or so