While taking a "doggie-bagged" styrofoam container from the microwave, only to find a portion of the container has melded with the food, hopefully gives enough pause that this food isn't eaten, others argue no plastic containers should be trusted. Some argue that microwaves shouldn't be trusted, as well.
Microwave critics warn that the way that microwaves heat the food causes abnormalities at the food's cellular level, which lessens its nutritional value if not more. For more on this argument, visit mercola. com's collection of articles or read The Microwave News.
As for microwaving food in plastic, many criticize that the plastic containers contain chemicals such as dioxins (which are toxic) as well as others, like Bisphenol-A (which is a synthetic estrogen that may cause early menstruation in little girls). For more discussion on plastic containers, visit The Minnisota Daily's article, or dr.mercola's compilation of links.
What's the alternative? A toaster oven and a tea kettle work fine for me. I haven't noticed a loss of time since tossing my microwave, and I use glass instead of plastic whenever possible. I save the pickle jars, etc. and I find those one quart canning jars have 1000s of uses, in lieu of those disposable plastic storage options. I find the food tastes better coming from the toaster oven, and it's actually faster to boil water for tea in the kettle than it was to heat the mug in the 'wave.