Anne Thompson over at the Risky Biz blog has a post about one of the "stars" of Borat. In this case, the guy isn't suing, but he still feels shafted. Don't just read the excerpt at Biz, read the full link as well.
I think the most surprising thing about Cohen is that he never reveals the gag to the victim. Imagine an episode of Punk'd where Ashton never comes out of the woodwork and you have to wait for the episode to air before you find out that you've been taken advantage of. Think that is a stretch? Given how Vanilla Face describes the "waiver process" and how much the filming was misrepresented, one could imagine some less than scrupulous comedian improving on Punk'd by having actor's sign any kind of contract under any kind of pretense.