I don't believe the Chemtrail stories, I for one am not spraying anything from the several aircraft I fly on a regular basis.
I will however not be drawn into a conspiracy theory's, I do believe Man landed on the moon, JFK was shot by a lone assassin, Monroe took a overdose, the World Trade centre was brought down by Aircraft, Elvis is still alive etc...
The other side of the argument can be found here...
chemtrails - contrails - The Skeptic's Dictionary - Skepdic.com
I have read quite a bit on this subject, I am afraid to say all the experts, seem to me to have no qualification in flight, meteorology, physics or climatology.
Please don't think I am sitting on the fence, I just don't have the time or the energy to argue against it.