The whole problem with this issue, is that "griefing" isn't necessary a compulsion. Griefing might only affect one person, a small group, or a single guild. Griefing might just be a person disliking another person and going to extreme lengths to disrupt that persons online life. Griefing, might not be considered griefing by each and every person.

How do you ban a thing that is experienced entirely different by each person. How do you define griefing? Is griefing, someone that has a spambot in a global channel, that responds automatically to certain words said in that channel, to try and provoke people into flame wars? Is griefing directly related to Trolling, or does it go deeper than that ?

All these things make me reluctant to say, ok, install a policy that punishes griefing severely. In my opinion, griefing is too subjective to be subject to a harsh policy.

If without any doubt, could be proven that a certain person made griefing his primary gameplay, I'd personally not go for the bans and account removal. I'd hit them where it actually hurts them ingame. Remove their entire flying mount skill and remove their flying mounts. They'd be struck ingame by more than just one effect. In raids they'd nearly always have to be summoned, they'd not be able to grind any money real quickly, not to mention any travel whatsoever. They'd have to put about 7K gold on the table again to get back what they lost and then they'd still not gain back their special mounts, such as achievement mounts and special drops.

Of course, this example only works for WoW, but nonetheless, every game has "something"that affects players ingame so much, that they'd never want to lose it.