I recently saw the SpeedTv show Fifth Gear/ Lethal Projectiles and they encouraged drivers to use a cargo net to restrain any loose items in the back of an SUV. I have a baby so this info really hit home.
Just knowing that even small items could become a life threatening projectile got me to install one. I got mine for my X3 from this place:
http://www.thecargonetstore.com
I tried the dealer but they are charging way too much.... Very well made product and makes me a little less freaked out when carrying something in the back. Just my 2 cents.....