It might impede your weight loss--some people find that it whets their appetites--but the preponderance of reputable research from peer-reviewed sources indicates that it won't poison you unless you have phenylketonuria.
Here's a link from
Snopes.com, the urban legends web site, that has some extensive information about aspartame. Included are links to articles from the Lancet, the FDA, MIT, Dr. Dean Edell, and Time magazine, all of which are valuable reading for anyone who's curious about the health risks of aspartame.
Pears, apples, and shiitake mushrooms (among other foods) also produce formaldehyde in minute quantities as one of their metabolites or contain trace amounts of it. It's a water-soluble compound, so if it's a concern to you in these foods, give them a soak before eating them. (I don't, but then I figure that if a trace amount of something occurs naturally in foods, my body's probably evolved to be able to cope with it--and if I'm wrong, then the mortician can just use less embalming fluid on me when I'm lying on his table.)
The link I used for the formaldehyde info was the
Hong Kong Centre for Food Safety, but if you Google other .gov and .edu sites, you can find some denser literature about it, if you're interested in deeper research.
