There is no need for a MAC address inless your planning on trying to hack something haha. You'll have multiple usernames regradless, a macaddress is normal tied to the router. So just look at the IP. While you can change your ip you can also change your macaddress. regradless if someone wants it they can have multiple users.
You can't. ARP (Address Resolution Protocol) is used to obtain the MAC when only the IP address is known. ARP is not a route-able protocol; there is no way you could get the MAC of a visitor to your site unless they were on the same network.
True that. The MAC doesn't go past the router, so the router will have your MAC in it's arp cache, and you'll have the MAC of the router in yours.
I dont have a router and I have had one and same MAC address for the whole time. Are you saying that the MAC address will change if I buy a router???
No, you can't change your MAC address. Every network equipment/PC/anything has a specific and permanent MAC address. Some with same brands have same addresses, but to rare occasions.
Yes, You can change MAC address by changing your ADSL Modem. Equipment with which u connect to Internet. I think MAC address tracking is possible by port scanning. Which can be avoided to some extent by firewall and antiviruses.