Restoring <= 10.6.8 lid-open Clamshell Mode in Mountain Lion?
You can get pre-lion behavior with:

sudo nvram boot-args="iog=0x0"


 
If it screws up your system, just zap the PRAM next boot (cmd+opt+p+r) and you'll be back to the default state. 

Or from terminal, this command will get you back to Lion's default state as well:
 

sudo nvram -d boot-args