I've only somewhat recently started publishing here on SOL, but I was a published fanfic author long before I discovered this wonderful sight.
I've had more than one story stolen, though never for profit. I'm always amazed not only at the sheer audacity of the plagiarists, but also at the response of the reading community when one of these glory thieves is exposed.
I suppose I've come to view it as a backhanded compliment, that they think my works are good enough to steal, even if I can't grasp the mindset involved. Though I will admit that I've pretty much stopped reporting when my old stories turn up under 'new' authors. There's no point. I know I wrote a good story, and if they need the ego boost that badly, then I suppose they're welcome to it.
Until Next Time.