This was a concern of mine too because I lift my current laptop by the corner all the time. Its a white plastic 12" iBook G4. Because its plastic it doesn't stay bent, but the casing is now a little creaky. I don't like creaky. So in I trounce into the Apple store to try these out. First off, the aluminum is more soid in general, but it is heavier. The MBA: no felling like its even going to think about bending, and its about the same weight as the iBook. The 13": really a good replacement for the iBook, solid, and slightly heavier. The 15": so heavy I would be a little reticent to lift one-handed, mostly for fear of slipping and dropping. The 17": this one looks rock solid and feels such to, but with that weight I think I caught a hint of considering bending. I would definitely not lift the 17 by the corner. I think the aluminum will outlast any poly case, if you take care of it. As MrCheeto's pic illustrates, dropping a unibody might cause more damage (vs poly) because the aluminum permanently deforms and is incompressable.