Aspartame (found in diet sodas) breaking down to Formaldehyde makes it to Mass Market front page news.
This was featured on Front Page News in Yahoo a few days ago. Rest assured that millions have seen it.
Its source was Rodale website.
"..a University of Liverpool test-tube study found that when mixed with a common food color ingredient, aspartame actually became toxic to brain cells. Making matters worse, aspartame is used in many diet sodas, and studies have found drinking diet soda may increase your risk of developing diabetes and metabolic syndrome. Also of concern with aspartame, researchers have found that one harmful breakdown product is formaldehyde. Sweet? We don't think so."
[link to health.yahoo.net]