Mountain Lion Users: Until this problem is fixed and if you get stuck in the monitor login dead zone...
Reboot your Mac while holding down the <shift> key. This will boot the system into 'Safe Mode' and then you can uninstall the DisplayPort driver so things function normally until this is addressed.
I just thought I would help out a few that I have read are stuck on screens not sure what option they have.
I REALLY wish there would be some kind of response to this problem? The radio silence is very very unprofessional. I think we are all just looking for 'Acknowledged and we are actively working on a fix'