Let's Talk About Teen Sex, Baby

So I wrote this post a few months ago but I never posted it for some reason! I think it's an interesting topic though so I decided to pluck it out of my Drafts folder.

According to the Kinsey Institute, about 65% of teens have sex by the time they are 18.

Whoa. Sixty-five percent? That's nearly two thirds! (I wonder what percentage of my high school class was sexually active? Perhaps higher than people were letting on.)

I've been thinking about teen sex today because I just finished Kody Keplinger's THE DUFF. If you haven't heard about this snarky/engaging/thought-provoking novel, then you might want to check it out.

THE DUFF follows seventeen-year-old Bianca Piper as her life goes down the crapper. Her parents are splitting up. Her dad is drinking again. And Bianca just needs an escape. So she starts a fling with her school's resident man-whore, Wesley, to forget about her troubles. (Even though Wesley initially dubs Bianca "The Duff": The Designated Ugly Fat Friend.)

And, yes indeed, there are quite a few sex scenes in this book. The novel doesn't get too graphic in its details (disclaimer: I've read numerous trashy romance novels so it takes a lot for me to blush!) but it still deals with the topic of sex very openly.

For Bianca, sex is complicated.
Sometimes it makes her feel dirty.
Sometimes it makes her feel free and alive.
And sometimes it makes her feel all of these things--free and wonderful and dirty--all at the same time.

Now that I've finished the book, I give big props to Keplinger for weaving sex into her story yet refraining from attaching an overt message to it. There's no "Sex is SO empowering!" or "Sex is SO bad!" stuff. Which I found really refreshing. Sex is a part of Bianca's life--just as it's a part of millions of teenagers' lives. Simple as that.

But some people disagree. After perusing the reviews on Amazon, I noticed a few readers thought that the sex was gratuitous in THE DUFF and not quite suitable for the YA audience. Certainly, this novel has stirred a lot of emotions and opinions in its readers!

So what do you guys think? 
What are the boundaries when it comes to sex in YA? 
Are there any boundaries?
Do YA authors have a responsibility over their readers in regards to sex? (For instance, Bianca and Wesley always practice safe sex in THE DUFF.)