Yes, you should be worried, but mostly about your coworker's fragile emotional state. It takes only moments to forward an e-mail to everyone whose address they've ever collected and I'm guessing they're thinking: I've just saved the lives of my 30 closest friends; whew, I need a soy chai latte.
The first microwave I can remember my family having was among the first ever made. I think it was a walk-in model, and weighed slightly more than both my parents put together. Perhaps that's an exaggeration, but I'm certain I recall my brother attempting to stuff me inside (today we get along slightly better). Now, I'm sure lots of radiation escaped from that model, which explains my grades in elementary school and our cat's raspy bark. But, today, microwave ovens are calibrated to fairly exacting standards and by all legitimate accounts, leakage rarely occurs except following severe damage to the unit (such as me kicking my way out).
As for the microwaves changing thenatureof food, the most commonly cited accounts in these e-mail warnings, on the surface, seem reasonable. The first references a university cautioning against warming breast milk in a microwave, and the second discusses a lawsuit involving a woman who died following surgery in which the nurse nuked the blood to be transfused. Here's where a partial story can be misleading. As we all know from trying to cook a chicken breast, microwaves heat unevenly-like Ryan-Seacrest-hair uneven. And that causes exceedingly high temperatures in some areas of food, or breast milk, or blood (if you're heating that last one at home, you should probably just follow your recipe). Those areas of high heat can denature(the word they were looking for)protein, which means it breaks the bonds within the molecule and can destroy it. Not a big problem in a Lean Cuisine, but definitely not what you want with your carefully breast-pumped antibodies or your surrogate red blood cells.
Plastics, however, are another thing. It doesn't take much to melt some plastics, just ask any 8-year-old boy with a magnifying glass (you can locate one by the smell). Unless they are made heat safe, most plastic containers like those used for butter, whipped toppings or cottage cheese will release a myriad of chemicals into foods heated by any method, including microwaves. Dioxin, most scientists agree, does not exist within the plastic and is only produced when it is burned (that's why that 8-year-old looks like Ukrainian President Viktor Yushchenko).
Microwave-safe plastic wrap is considered relatively safe, as long as the plastic doesn't touch the food, especially greasy or oily food. Not an easy task given our culture's desire for super-sized portions of delicious fatty fare. So, a better solution is to cover your glass or ceramic bowl with waxed paper. You've probably got some leftover anyway from a fruitcake you re-giftedthree or four Christmases ago, so you might as well use it up.
I think we've got better things to worry about than the microwave, such as the actual food we put in it. But, if you're really still concerned, there is one sure way to ease your mind: Change your e-mail address.