I'm the type of person that doesn't care if I'm plagiarized in any way--it just feeds my ego a bit. If they're stealing my work and calling it their own, then I'm just that much better than they are. The fun comes if I happen to catch them in the act, because then I get to disgrace them in a public Internet space. I do happen to enjoy outing people who are plagiarizing others, however.

I.

In this situation I would screen shot the appropriate information, and then plaster those images all over the role-play. Oh, before that I'd have to write a nice little message thanking the person for the flattery.

II.

Wouldn't care. I'd probably make fun of them a bit over messenger or something.

III.

It's the GMs fault, and I'd pretty much do exactly as I did in situation one. Point out how I made the character, and make the people responsible feel stupid.

There's no point in getting upset about this sort of stuff. It's better to just make the other person look like a lame phony, and have a good laugh at them.