Do I think the bad guys will be using their own devices? No. The seriously bad guys have many different encrypted or hidden methods of communication, this will only affect the rest of us. Do I think McDonalds keep a record of every MAC address that accesses their WiFi? Probably not, maybe, but its certainly not impossible, and if you access Telstra WiFi or similar then you can expect it to be retained. The MAC address isnt the only thing that necessarily identifies a user or device either.