Thin and Light Laptops Could Have Design Flaw
Plastic isn't good enough for the new thinness.
Aside from the Apple MacBook Pros and select premium PC notebooks such as the Voodoo Envy and Dell Adamo, nearly all computers today are made from plastic casing.
While plastic is a good material for notebooks because it is light and easily molded, it's not particularly rigid. This is a problem that some computer manufacturers are now finding, according to comments made by Broadpoint AmTech analyst Doug Freedman.
CNet quotes Freedman, saying, "Early production units being built in plastic, with the bottom case being plastic, are cracking. … So, to get that really thin form factor that they're after, they're probably going to have to go with a metal case."
Computer makers are currently trying to make thin and light laptops based on Intel's CULV chips (consumer ultra low voltage), which pave the way for affordable thin and light notebooks. The problems aren't to do with the chips, however, but rather the form factor that the new hardware facilitates.
With apparent problems with using plastic, switching to metal would likely drive up prices of the notebooks that were meant to come into a price point that's affordable for the mainstream consumer.
It'll be interesting to see the type of design solutions that ODMs and OEMs come up with to try to solve this problem.

This has been another update from the common sense brigade.
The problem should be the tendency towards the use of lowcost materials. With high grade ABS this probably wouldn't happen.
that should prevent cracking from the sensitive points
This has been another update from the common sense brigade.
Joking..
Anyway, I would love to see new laptops using aluminum and some hybrid mix of plastic/metal through the case. This would give us new looks and the color of those different materials would be something that can catch our attention and desire.
I Lol'd.
But as a structural engineer myself I can see that fatigue is most likely the cause, after all, constant heating-cooling cycles combined with very erratic load patterns can impose quite a strain on brittle materials.
I ment to say I can see why they would crack and I'd guess that fatigue is most likely the cause, as opposed to strain caused by the laptop's weight.
I agree, just put where the most weight is or where two pieces of plastic join.
Almost every single one was due to low quality material and poor but shiny design
They(manufacturers) know about that and every single one hides those information from general public.
Thin & light are VERY VERY thin notebooks (because 1" is just too damn thick) so there is less structure to work with. Also such notebooks have a 13" screen, usually no optical drive, but the ThinkPad X300 does.
The Netbooks are very small overall and very light-weght and shouldn't have the issues of its more expensive cousins.
Want a notebook thats going to last, get a ThinkPad. They have a FRAME under its skin and other features that make them tougher than most other notebooks. And they aren't as expensive as they used to be, starting at $550... yet they do have their $2500~3500 17" dual screen models