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Dropping Gear 30-Oct-2003 At 2:33:50 PM The Blond Gecko

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Going way, way back to my materials science course in my undergrad days...

Alloys such as these are tempered specifically to have very small crystal sizes (a few tens of microns). Cracks essentially only form and travel along the fracture planes of crystals. Thus, if a crack forms in one of the crystals, it will only travel across that crystal, before being stopped at the boundary. Aluminium is also naturally relatively ductile compared to steel, meaning that it will stretch, bend or dent preferably to cracking. Steel, on the other hand, has a relatively high ductile-to-brittle transition temperature (depending on the specific alloy used), often above freezing. I remember hearing about some early US navy ships breaking in half in cold water due to this. In addition, it's much more dense than aluminium, so a fall of equal height will develop a whole lot more force when it impacts. I wouldn't use anything steel that I'd dropped from a significant height, but I can't see any problem with re-using aluminium items (within reason).
A bit of a ramble, but hopefully useful.

Cheers,
Tristan