[rileyteige]

MAC address would work for this, no? Wouldn't solve the spoofing but solves the dynamic IP address issue.

[IiydAbITMvJkqKf]

MAC addresses are not exposed to web sites, and for good reason. It would be the mother of all supercookies.

[charcircuit]

Wouldn't a supercookie like that make things more secure though? You could even use it for fingerprinting to help combat things like spam.

[jaywalk]

MAC address cannot be seen past your local gateway.

[stedaniels]

MAC addresses aren't sent over the Internet.