According to [Wikipedia](http://en.wikipedia.org/wiki/MAC_address):

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> A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment
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> 
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But how unique are MAC addresses on devices coming out of the factory? I seem to remember hearing a long time ago about how some manufacturers would reuse MAC addresses on their network cards. Does anyone have any hard facts one way or the other?