A couple of high school students did an experiment using DNA testing to determine whether foods bought randomly around Manhattan were in fact what the label claimed. 11 of the 66 foods they tested were not, including sheep cheese that was really cow cheese and sturgeon caviar that was really from some inferior North American river fish.
The article I'm paraphrasing above is almost a month old, but I just read it for the first time re-printed in the local paper. Another compelling reason to eat locally and get to know your growers. Some common food fraud mentioned in the article included honey watered down with corn syrup and olive oil that is really flavored and colored soybean oil. The FDA, of course, is too overwhelmed to do much about it. Read the full article from the Washington Post here: http://www.washingtonpost.com/wp-dyn/content/article/2010/03/29/AR2010032903824.html