I've tended to stay away from reporting about players angry at being banned, for reasons I'll get into in a second. But we periodically receive notices from players who think they've been unfairly banned, and there's lots of forum complaining on the same subject. The complaints have been loud enough, it seems, for CNET to take a look at the allegations, and get a nice quote from Blizzard about it.
Most of the angry players (if you are one, feel free to leave a comment below with your own story) say they try to log into their account one day and are simply banned for no reason at all. Some of them say they've even had their accounts hacked, and are then finding them banned afterwards. Most of them, in my experience, sound just like Zak, a 14-year-old interviewed in the article. He says he was banned because "I was leveling excessively and very fast, which is what power levelers do." One day he had an email in his inbox that said he was kicked out of WoW.
CNET then does what all of these players haven't seemingly been able to do, which is get a response from Blizzard about the whole thing. "We conduct a very thorough investigation before the actual ban takes place," says the Blizz spokesman. He says all bans are carried out only once Blizzard has decidedly determined that there has been action that goes against the Terms of Service and/or the End User License Agreement (that's the long text which pops up after you install every patch).
And the reason I don't have a lot of pity for the people who say they're unfairly banned is that I, for one, tend to believe him.