We plan on declining any testing (other than the 19wk ultrasound). Our OB has a philosophy we agree with....he always says "if you found out something was wrong with the baby, would you terminate the pregnancy?" If the answer is "no," then there's no point in getting screened. Plus, as a previous poster said, the false positive rate is really high. Our friends got a false positive for Downs just a few months ago and were so frightened they went ahead and had an amnio. Amnio showed things were fine, but then they worried about the amnio causing a m/c. Tests just cause worry, in my opinion.
BTW, our twins have a non-inherited genetic illness (one that doesn't show up on any of the typical fetal screenings), so we've been up close and personal with the "something wrong with the baby" issue. I found with this pregnancy (personally) that it's a lot more reassuring to meet with a genetic counselor and discuss the risks than it is to submit to a hundred different tests and fetal screening. Talking to a counselor, we found out there's a 1% chance of the same illness affecting this baby. 1/100 odds are something I can live with.