"Under the food additive provisions of the Federal Food, Drug, and Cosmetic Act, new substances used to make plastics for food use are classified as 'food contact substances.' They must be found safe for their intended use before they can be marketed.
"'It's true that substances used to make plastics and leach into food,' says Edward Machuga, Ph.D., a consumer safety officer in the FDA's Center for Food Safety and Applied Nutrition. 'But as part of the approval process, the FDA considers the amount of a substance expected to migrate into food and the toxicological concerns about the particular chemical.' The agency has assessed migration levels of substances added to regulated plastics and has found the levels to be well within the margin of safety based on information available to the agency.
"'The FDA has seen no evidence that plastic containers or films contain dioxins and knows of no reason why they would,' Machuga says."
Finally, the FDA says that "generally, microwave-save plastic wraps, wax paper, cooking bags, parchment paper and white microwave-safe paper towels are safe to use"
http://www.breakthechain.org/exclusives/dioxins.html
and btw, i know im not supposed to but i still boil water in the microwave...