After opening up the bottom half, the bottom of then ote book is magensium alloy, I there are a few other parts that I think might be, but I do feel some of it to be plastic. However, i do have an issue with magnesium called corrosion.
Me being into Mt. Biking a great deal we've learned some thing about material useage, specifically on metals. Steel, aluminum, carbon fiber, magensium alloys, titanium alloys...ect. All have their special characteristics, but magnesium is seen often because of the light weight and great strength compared to steel. We use it in the suspension forks mainly for those fact, but also because mag. is very stiff too, giving better steering percision. However, during the first few years it was used they found a huge issue with long term integrity of the metal because of its high corrosion rate. We found that painting on the outside helped, and that them movement on the inside kept it from corroding, so it is is still used today.
I know that the outside of my computer is painted, but a quick check inside proved that the interior isn't, so it is free to corrode. In this situation though, I doubt it will make much of a difference. The estimated loads of this unit are doubtfully going to see what my bike does when I huck it up off the loading docks by wal-mart. Totally different scenario, but something to think about none the less.