I agree with this. You said that like to know that it was stolen, but what if you don't even know? What if people are enjoying you're build without your knowledge so you benefit in absolutely no way.? How do you feel about that? <- Dr. Phil :P
If there was someone out there who happened to have one of my builds, and I didn't even know, then really I guess, since I didn't know someone else had it, I wouldn't feel anything about it. :S
Although, I understand what you mean. I'd just be glad that people are getting to see my stuff and play on it, even if someone else is hosting it without permission, or claiming it as their own.
They could claim it as their own all they want. People are getting to use it and have fun with it, and that's all that matters.
Plus, if I was confronted on whether I had built something of my own, that someone had stolen and claimed as their own, I would say "Yes, I did build that". And if they didn't believe me, I wouldn't go out of my way to prove them. I'd just be happy with it. I can allways build more stuff. And usually, people have seen the stuff I've built.