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.