Account bans are toothless and users know that judging by the amount of people who re-register, they need to ban by IP. It has the unfortunate side effect of potentially affecting legitimate users but the odds are generally acceptable if you use the proper octet.
Unfortunately if a user really wants to evade a ban it's difficult to prevent them (proxies, VPN, etc) but most people will give up before that unless they're very determined.
Playing: Dark Souls 2: Scholars of the First Sin Watching: Mr. Robot