IIRC MS used to ban people with modchips from Xbox Live based on the MAC Address...that's possible for Sony to do it, but as I understand it they do not.
Yes, MS is still active in banning Live accounts and the consoles themselves.
I wonder if they do track PS3s. It'd make sense that they'd put in a system to ban specific PS3s from the system, but that doesn't mean they've done it.
Sony has stated before that if you prove to be too much trouble, they do have the ability to ban your psn account, machine, and IP. Therefore, you would have to purchase a new PS3 and move if you wanted to use the PSN again.
If you want a link to the source, I will have to provide it later as I am at work.