How tough is the aluminum body of a MacBook? I had an older macbook with a plastic shell. I broke and replaced the screen several times  over it's lifespan.

I now have a MacBook with an aluminum body and am really nervous about cracking the screen.

Should I be that nervous? Have you seen an aluminium cased MacBook with a cracked screen?

Is getting a "MacTruck" case overkill?

Update: 20 months of use with a thin Speck case and no cracked screens.
The unibody construction is substantially more impact resistant than the previous plastic design. This is especially true in the display area where the front glass and the rear aluminum act more like an I beam than the old design. Not only is the construction more sturdy, but in falls, the damage tends to be less expensive to repair should you actually break things.

For example, the unibody macs with enclosure damage usually cost between $300 and $400 to repair where a cracked screen can cost upwards of $800 to $1200 for an Apple repair. The unibody parts require better tools and training to repair inside them, so that's about the only down side I can see to the newer design. Aluminum is really much stronger than the old LCD panel with thin metal braces and a plastic shell to cover the display. Even the new macs with matte displays are much stronger than the old pre-unibody displays on MacBook Pro / PowerMac line.

Of course, many single falls can break even the expensive parts in a unibody mac as the tolerances inside the machines leave little room for deformation to safely absorb the shock of a fall, but I have seen far more unibody macs that have skidded across pavement at highway speeds that still worked and had only surface damage than the previous generation of non-unibody macs. (Yes - it happens more than you might guess and when placed on the top of a car or truck, sadly they don't actually leave the vehicle until you get up to highway speeds. Now the ones run over by a following vehicle - unibody stands up better, but still doesn't usually survive that ordeal.)