A coworker of my DH's wife had the NT which came back positive which was 1/99 (I think, I looked it up, but couldn't find anything) all because she was over the magical age of 35. But everyone freaked out and had the amniocentesis done and it turned out that everything was fine and they had freaked out over the waiting period for absolutely nothing.
We didn't do the NT scan for DD, and I won't for this one either. My reasons for thus is this: I was 29 when I became pregnant with DD, I am 32 now. My DH and I are from different background neither of which is considered high risk for down syndrome. (I'm told that in Québec, south of the St Laurent, there is a higher risk of DS in that population. And since we live in Ottawa, they did ask if we were from there.) I do get the 20 week anatomy scan done just to make sure everything's okay and to make sure that the placenta is not in the wrong place and to find out the gender.
It really boils down to what you're comfortable with.
Would you terminate the pregnancy if you found out your child has Down Syndrome?
Are you willing to do an amniocentesis that carries a 2% risk factor for miscarriage if the NT scan comes back positive and that's what they want you to do next?