I rally hate it when people so easily dismiss things. Tests from residue, and yes, there is residue which you can usually find strung all over your car in the early morning before the sun melts it, has been shown to contain high amounts of boron. Personally, I think they are just doing weather experiments. I've heard theories that they are trying to lower global warming effects by producing boron clouds to block out sunlight/radiation. Anyways, if you're still skeptical, check out
http://www.carnicom.com/contrails.htm