We saw it w/ DD (12) and DS (6) on DD's b-day. I read several reviews for parents beforehand, and was on the fence about taking DS along with. Then I thought about it...he is a big time Star Wars fan and has seen and enjoyed a few of the LOTR movies. The violence in the film, I felt, was considerably less than any of the LOTR films. There is some objectionable language , but not anything more than any other PG-13 movie that I've seen lately. There is one "sex scene"...more insinuated than shown. No nudity....well, scantily clad, but we're all pretty used to breasts around here

and none are bared in the film. Since they wear loin cloths, a little bit of butt on occasion, but we all have one.... Honestly, for me, violence and language are a bigger issue than nudity...so maybe for some the "digital skin" is a deal-breaker.
Now that all that's out of the way..... I don't regret taking the kiddos to see it. It was phenomenal. The animation was absolutely seamless. I couldn't tell where CG ended and live action began, in regard to landscape. The plotline did provoke interesting discussions re: the perceived "right" of a powerful nation/company to take resources regardless of cost to the eco-system/indigenous population; what your "spirit" identifies with vs. what body/culture you are born to (if you see it that will make more sense-this actually led to a discussion of gender identity, which was cool), and the kids wanting to find out much more about how CG rendering is done.
I only wish we had an I-Max or 3D theater nearby...it's probably unreal in 3D.
So, I guess it's like anything else. You know what your 8yo has seen/read and what your comfort level is....Hope this helped. And if you go, get an aisle seat...it is freaking loooooong.