obviously, this isn't a pr0n site, and hentai isn't our target content. however, it would be foolish to think users won't upload hentai on their own. that said, it could be argued hentai is still a part of the anime canon (if loosely), but i'm not about to be a pundit for it's inclusion...
We talked at one point about (someday) having some kind of way to tag adult content so that it can't be viewed by users whose birthdates said they were under 18, but obviously that'd just be a butt-covering tactic, and who knows if it'll ever actually happen. The thing is that it's REALLY hard to separate out the porn from the mainstream, largely because so much mainstream (non-porn) anime is developed out of hardcore pornographic games. I mean, if you look at the fall anime season alone, two of the anime are based on eroge (erotic games)...and that's a low number compared to some recent season.
Back on the topic of tentacles, funny story-- one of the reasons why they're so predominant in hentai is because when we occupied Japan after WWII, we put a bunch of obscenity laws into place which prevented Japan from being permitted to show genitalia (to this day, pretty much all Japanese pornography, real or animated, has naughty bits mosaic'd out). But a tentacle is just a plant! Or an alien! So it was allowed.
I think the adult tag might not be a bad idea just to cover yourselves. I like animes better when there is nudity allowed. It just seems odd that whenever there is a seen in a spa or the like there is mysteriously a cloud right over the private areas.