dr_lha said:
I believe it is necessary for how TCP/IP networking works for any network card to have a individual MAC address which is unique to the card. This has the downside of course that you can effectively track what computer internet traffic is flowing to and from if you have the ability to intercept packets as they pass through routers, as the AT&T and the NSA are allegedly doing. Note, its not clear that Apple know the MAC address of your Mac, they know the serial number. Of course they installed the card so they may or may not keep a record of what MAC address matches what Mac.
Thats not entirely true. TCP/IP doesn't care about MAC Addresses, only the ethernet hardware does. If you look at the TCP/IP header (google for it), you'll see the MAC Address doesn't get sent out in any packets.
So really all you need to do is make sure that any devices on the same ethernet network (not bridge by an IP router, for example) don't have the same MAC Address. To eliminate this possibility altogether, manufactures assign each individual card a guaranteed unique address, and each manufacturer has their own unique prefix.
My guess is that Apple does record which MAC address gets installed in to which computer. I've seen MAC addresses printed on invoices for other computer manufacturers, so Apple isn't that different.
But its nothing to worry about. Very few networks are tracking MAC Addresses and recording them. Of course, most sites *are* tracking IP Addresses, and if they contacted your ISP your ISP probably has a record of which MAC Address was using which IP address at any point in time, and so network traffic can be traced back to you in that way. But most network interfaces can have their MAC address manually overridden if this tracking possibility really concerns you. My opinion is just dont do anything extremely illegal and you have nothing to worry about, plus when people are using the internet to do extremely illegal things, the feds have at least one way to try to track them down.