Is it safe to use plastic wrap in boiling water?
Agree with ceejayoz that melting isn't the issue.  Melting is just the upper bound for problems.  The common concern is about leaching, the diffusion of chemical toxins from the plastic into the food.  It's known to be accelerated through fats and at heat, hence the concern.  There seems to be consensus that "some" leaching occurs; the issue is that it's unclear how much, from which plastics, whether the body absorbs or excretes it, and if it matters. 

Alarmists will tell you that the chemical run-off is toxic and causes everything from cancer to birth-defects.

Governments have looked into the issue but not come out with a hard no.  Industry groups are fighting the issue, but losing public opinion on things like waterbottles (see nalgene, which removed Bisphenol A (BP-A)from their formula).

Chefs generally care more about results than fringe chances of non-lethal toxicity and they have been using plastic wrap for as long as it's been around.

What should you do?  It depends.  Weigh fear with convenience.  Use good quality products if you do use it.  Don't do it too often. Or just enjoy it.