I do not know much about networking, but I do know a bit. MAC addresses usually aren't random and therefore are specific to the device used to connect. That doesn't mean you can follow them always everywhere, two problems arise. As far as I know, the MAC addresses do not leave the local network. This would mean connections from open APs probably cannot be traced to a home connection/ISP. The second problem is that MAC addresses can easily be spoofed, it's built right into most if not all operating systems.
In regards to data tracking: a Wifi router saves information about which MAC address had which IP at a certain time. How much logging is usually done and how this relates to the ARP cache, I wouldn't know. As MAC addresses can be spoofed and are hard to trace and IPs are temporary and random, the best bet to actually finding someone would be identifying traffic. WallShadow had a great post about it
here.