I think it's been called in some circles the "90-degree to pitch black" problem. Many can mistaken it for a faulty logic board, but with symptoms like this it's actually caused--at least from what I've read from numerous accounts--by a worn out reed switch cable which connects to the logic board. Here is a pic o the part I'm talking about:
(Edit: the portion up top with the black sleeve is the inverter cable which plugs from the inverter board to the logic board from the bottom right plug, and the bottom left is the reed switch which is activated when you close the lid to your desktop by a magnet right below your keyboard on the right hand side. You'll find it with a paper clip under the right arrow key)
Symptoms are the screen flickers in dimness as you move it back, sometimes dropping out all light when the notebook is opened all the way. The only way to achieve full brightness is if you open the screen at a 90% or less angle, which is a killer on the neck.
In addition, another problem people have been running into which is caused by this very same switch is when the lid is shut on the notebook, and at random instances the notebook wakes from sleep by itself. I've waken up night to see light seeping through the close lid from the display because the machine had awaken from sleep without anything or anyone touching, just by itself.
Apple had quoted me a price of almost $300 to repair the thing, after bringing the system in one of the store employees insisted it was a logic board problem. I got a call next day about what the problem was, but I told them not to fix it. I'm getting the part from smalldog.com for $20 plus $7 shipping and installing it myself.
Here's the
tutorial that I'm using right now. If you have the same problem, this is a great site to check out, but one word of caution: use some common sense when disassembling the machine, because there are some extra steps you need to take which are not mentioned in the tutorial. One of them for instance was disconnecting the ghost light from the stiffening frame.
Pbfixit.com is also a great resource in looking up parts for Apple notebooks. If you wanted to, you could technically swap out the logic board for one with a faster G3 processor, but it will cost anywhere from $300 to $400. Check it out:
http://www.pbfixit.com/cart/customer/home.php?cat=50
I will post the status of the repair once I get the part. I might be ordering a 5400 rpm HD from newegg.com while I'm at it.