A friend of mine's account was banned because she was warning people on Twitter about Aaron Brown, now going by "Timmer", who was convicted of wire fraud and embezzlement, as well as lost a lawsuit after defrauding a charity, then left the US to escape having to pay. He's highly active in the Barcelona area, professes to be a wine expert.
She's been following his activity on twitter, and tweeting people who interact with him, warning them about him.
Bam - account permanently deactivated a few weeks ago. Gone. All her tweets, years worth, gone. Nobody to talk to, nobody to appeal to, no process. Account disabled, end of story.
Twitter is now allowing scammers to use its anti-harassment policies to silence people warning others about them. Good job, Twitter...