Hello all!
Lion has changed to default behavior of the internal screen from the old functionality in Snow Leopard. Previously, in SL (Snow Leopard), a Mac with an internal screen could be connected to external mouse, display, and keyboard and be ran with the external as the primary monitor WITH the laptop screen open. It is important to keep the screen open on laptops to release heat. Here are the steps to restore this functionality in Lion:
I have found that this command in Terminal restores Snow Leopard functionality in Lion to closed-lid/clamshell mode.
1. Open up Terminal in /Applications/Utilities
2. Type the following command: sudo nvram boot-args="iog0x0"
3. Press return
4. You will see a warning about using the sudo command. PLEASE make sure you typed the command into Terminal correctly. Mispelling sudo commands can be... dangerous.
5. Type in your password to confirm and press return.
6. You should see Terminal move to a new line.
7. Restart your Mac and the Snow Leopard functionality should be restored!
Note: Resetting the PRAM will erase this modification. If you are ever told by Apple to reset the PRAM or need to do so for another reason, you will have to repeat these steps again. The mod holds as long as the PRAM is kept intact!
If the command did not work after restarting, reset your PRAM by holding Command, Option, P, and R after turning your computer on. You can release the buttons when you see the screen light up.