I cant speak on all measures blizz has in place, but 2 that hawker has confirmed is MAC and HDD serial.
I'm sure they track tons of other things as you could easily spoof a mac, as you mentioned. (Or use VM to get around HDD).
I'd love to see a post from Hawker about this as it is complete and utter nonsense (I was gonna use a stronger word but thought the better of it).
Blizzard isn't allowed to read your MAC or HDD serial from your PC. They simply can't do this. It's against the law (well, at least it is here in Europe). They could use the MAC of the system connecting to their servers but all they got there is the MAC of an ISP router which wouldn't really be smart to ban (anyone on cable in the Netherlands will eventually be on the same ISP so they'd be banning just about all Dutch players; not a smart thing to do).
No, they don't ban on IP, but they can use it to help their investigation.
No, they don't ban on MAC. Not only are they not allowed to read the MAC from a local NIC, not only are they easy to spoof, they are also NOT unique (there was a series of popular NICs in the past that all had the exact same MAC address.. You wanna take the risk of banning all those people? Millions of those were sold.....)
No, they don't ban on HDD serial. Again: Against the law, again easy to spoof (yes you can change the hwid reported serial), easy to change (replace the HDD and you can't be tracked?), easy to manipulate (use a VM and suddenly you have the same serial as a million other people).
A computer doesn't have any information that Blizzard is allowed to read that can identify the player. Not so strange as that's exactly what European privacy laws are supposed to protect. Any information that can identify the player (outside the information necessary to log on to the service) is protected by privacy laws and thus off limits.