Tim kindly provided us with some links and commentary.
Environmental Working Group on Perclorates: http://www.ewg.org/reports/suspectsalads
A pdf of their report: http://www.ewg.org/node/19342
Here's a pretty cautious article about iodine/thyroid/perchlorate, with plenty of references: http://www.vrg.org/journal/vj2006issue2/vj2006issue2iodine.htm
maplight.org connects data on campaign contributions, politicians, votes, industries, companies, and more to show patterns of influence that could never be seen before
Lawrence Lessig explains money and politics, relying heavily on maplight.org:
http://longnow.org/seminars/02012/jan/17/how-money-corrupts-congress-and-plan-stop-it/
My summary, which you should factcheck before you jump into public discussion or out of an airplane with it:
Perchlorate is in solid rocket fuel to provide oxygen to the fuel mixture. It's hydrophilic and goes stale, then they pressure-wash it out of the tubes. It goes into groundwater plumes and rivers from military and industrial sites. For example the spaceshuttle solid rocket boosters spew vast quantities all over the southeast at launch time. Vandenburg Air Force Base missile launches spew perchlorates into California's Central Valley.
Perchlorate levels in irrigation water from the Colorado and other rivers are above safe levels. The leaves of crops concentrate it further through evaporation.
Your thyroid can't tell the difference between perchlorates, nitrates, a few other things, and iodine. Your thyroid uses iodine to make hormones t3 and t4.  Americans are low on iodine because it's not in sea salt or junkfood salt, so your thyroid uses the other things instead of iodine.
Your body says to your thyroid, "gimme t3 and t4".
Your thyroid says, "I have this fake t3 and t4 I made out of junk."
Your body says, "that stuff is fake. give me t3 and t4."
Your thyroid says, "I have this fake t3 and t4 I made out of junk."
Your body says, "It's fake again. give me t3 and t4."
So your poor little thyroid gets all exhausted making counterfeit hormones out of non-iodine pollutants and you get hypothyroidal.
Fat, lethargic, depressed, dry hair.
Yes, the American character is the same thing as perchlorate contamination.
The solution for individuals:
Eat lots of iodine such as the kelp drying in my car's back window.
Avoid leafies from unknown sources, especially those irrigated from the Colorado River and especially the Imperial valley. Wintertime is when that area dominates the market.
Organic greens can be just as bad. The highest
levels sampled were in a bag of "organic baby spinach".
Avoid preserved meat.
Eat iceberg lettuce. It's got the lowest perchlorate levels because there's less evaporation. Also it's more fun and you can pretend you're eating crispy green brains.