One thing I personally noticed with these types of "cast-looking" parts is that they tend to fail in a brittle way and there's really not much ductility. I've seen many notebooks with Mg alloy casings that shatter when dropped, and I've always preferred the Apple unibody machined aluminum for this reason - if it's bent or drops, it tends to retain its integrity much better. Granted, aluminum doesn't tend to have all that much ductility before it too, breaks, but I've found it more robust.
