I've seen porn. I've seen bang brothers films/clips that got uploaded. I've seen amateurs put up stuff. Doesn't generally stay up long, but I've caught it once or twice. Though I've also never come across it accidentally, only seeing it when a friend or acquaintance links it.
And as I understand it, non-pornographic nudity is ok. So like health-related videos are fine (though makes me wonder, how they would treat a health-related video that, for example, was talking about and demonstrating masturbation). Though like you, the only nudity I've intentionally come across has been exposed breasts.
Although I did once come across a home birth video.. that was interesting to see.