Well, it's been a long while and I've given it thought for a long time.
DA is one of the largest art sites out there. It's just begging to have things stolen from it and it does have things stolen from it. Every day. People know to come here to get art to sell, even if they aren't allowed.
DA won't help you stop them, or get your art back. DA also promotes tracing and theft to a degree.
Though I can attribute half the theft to stupid kids who like to think their art isn't worth stealing, or great artists who don't like to watermark, talk about being too modest for your own good; or just stobbon to a point of stupidity, watermark does not = ruined picture. I've seen people who barely put a worthwhile watermark on their stuff even though it has been stolen before; seriously, grow a goddamn brain; and don't breed please. Ever.

But I don't use DA much/because it's a crock-pot for art theft. Say what you want to defend it, but not hearing the truth doesn't make it untrue.
Defend your art, if you don't you deserve to have it taken.