I probably should have read the thread rather than replying about weak plastics as I was asked to 
anyway- yeah- the bad hinge design is less of a "bad hinge" design and more of a "metal hinges connect to plastic (lack of) frame"
the main design flaw is that apple designed the LCD assembly to depend upon the rigidity of the back and front being held in fixed relation to each other due to the upper lcd screws such that the 2 of the lower screws that go from front to back sandwiching the hinge plate do not get trapezoidal flex.
this is fine and dandy, but the eventual breakdown of grey abs (moreso in the black plastic of the 550), removes the slight springiness that it has, so when the screw posts are flexed, the mount wall surrounding them slowly tears apart.
Once this has happened, the lcd still opens and closes, but it feels weak. at this point, the hinge is relying on ONLY the secondary screw posts which attach to the bacl cover only. this mount point has no bracing or support from the front cover, and as such, will eventually rip through as well, with usually more disastrous results.
preventative measures would be attackign the back assembly and hinge plates with some metal filled epoxy and ereinforcing the outer ring that holds the screw posts, or more drastically, affixing the entirety of the hinge plate to the back lcd. while the second solution is FAR more damaging if you are going for "cllector" value, if done right, the hinges will fail at their base before the lcd panel ever takes damage due to the massive surface area potential of the hinge plates.
anyway- yeah- the bad hinge design is less of a "bad hinge" design and more of a "metal hinges connect to plastic (lack of) frame"
the main design flaw is that apple designed the LCD assembly to depend upon the rigidity of the back and front being held in fixed relation to each other due to the upper lcd screws such that the 2 of the lower screws that go from front to back sandwiching the hinge plate do not get trapezoidal flex.
this is fine and dandy, but the eventual breakdown of grey abs (moreso in the black plastic of the 550), removes the slight springiness that it has, so when the screw posts are flexed, the mount wall surrounding them slowly tears apart.
Once this has happened, the lcd still opens and closes, but it feels weak. at this point, the hinge is relying on ONLY the secondary screw posts which attach to the bacl cover only. this mount point has no bracing or support from the front cover, and as such, will eventually rip through as well, with usually more disastrous results.
preventative measures would be attackign the back assembly and hinge plates with some metal filled epoxy and ereinforcing the outer ring that holds the screw posts, or more drastically, affixing the entirety of the hinge plate to the back lcd. while the second solution is FAR more damaging if you are going for "cllector" value, if done right, the hinges will fail at their base before the lcd panel ever takes damage due to the massive surface area potential of the hinge plates.