To clear a few things up about these fatigue cracks that you are all seeing -
The cracks that you are seeing in the lid are indeed caused by opening and closing of the lid. The reason that many of you are getting cracks in the same location isn't happenstance. The stresses induced by closing the lid are greatest near the base of the lid. Fatigue cracking is preferentially initiated at the little ridge just above the base of the lid due to the stress concentration caused by the ridge.
If you do get cracking in that location, you *can* fill it with glue, but I wouldn't suggest it. The closing tractions induced by the glue likely won't be significant enough to delay further cracking by a reasonable enough time to justify the risk of gluing up your expensive laptop. In addition, the glue could simply be fractured (depending on what type you use) by the compressive stresses when you are opening the lid.
As for the screw issue, I doubt it's from the screw being over-tightened. There are stress concentrations associated with the hole itself (not to mention any threads inside the hole). The hole will also preferentially initiate fatigue cracks. I haven't seen any pictures, but I doubt that those cracks were there upon receipt of the laptop. They are due to the same phenomenon that's causing the lid cracks - fatigue.
Opening and closing your lid repeatedly will accelerate the cracking process. What I would suggest, if this is unavoidable, is to open and close your lid slowly and carefully, by the middle of the lid. This will greatly reduce the stresses on the lower edge of the lid.