I am just betting on it since I am not buying another "official" Ethernet anytime soon. I was rather shocked when I got my Ethernet Shield and opened up the ChatServer and my unique, one of a kind MAC address was already entered for me. Only two possibilities, I somehow got David Millis or Tom Igoe's Ethernet Shield or the MAC address is just a safe resting place for developers (especially the high serials of EF:FE:ED).
If anyone wish to verify their "official" Arduino Ethernet MAC, I would love to confirm my theory.
Anyhow, if you run inside you home network, you will be fine with any unique MAC as long as you are behind your router. You will just need to open a port on the router to access it from the outside or get a home server up for Arduino management. Arduserver is a good starting place
@Coding Badly
What does your Ethernet Shield MAC sticker have on it? Mine has 0xDE:0xAD:0xBE:0xEF:0xFE:0xED which is identical to the ChatServer sketch.