just noticed that since the lion update the ambient light sensor no longer works.
Try resetting the SMC Controller.
Shutdown, and hold Control+Option+Shift, then press the power button. I just noticed mine wasn't working after reading your note, and I did this, and now it's working.
How do I know if the ambient light sensor isn't working?
In a bright room (or screen facing the window), hold your finger in front of the camera opening. The display should dim noticeably.
btw: my sensor works just fine @ 10.7.2
but this is only if one has selected the 'automatic light adjustment' option in the display section of system preferences, right?
mine is not selected, so there should be NO automatic dimming, right?