honestly, the big thing for me is not things like dookie and such, but the line that is crossed when one or more participants are deliberately degraded. BDSM is one thing where you can tell the sub is enjoying the hell out of the situation, but when someone is getting slapped around and the like, I think the act has stopped being erotic and has become obscene.

I big one in straight "gonzo" content is something common to European productions (example: Rocco Siffredi) where the female model is being sodomized doggy style, with her face on the ground (or couch, or whatever) and the male model puts his foot on her face. It strikes me as so damn degrading it's nauseating.

my $.02