We actually gave up on microwave popcorn after the numerous articles kept coming out about the health hazards. I dont' know if those warnings are overblown or not, but now that we've switched to air popper, we realize we much prefer the taste.
Anyway, health concerns might be able to be avoided:
If there is any danger at all associated with microwave popcorn, it is most present when the bag is first opened and heated fumes escape. Breathing in these fumes will expose the consumer to the highest level of diacetyl possible at the consumer level. This may cause damage to the smallest air passages in the consumer's lungs or trigger a pre-existing asthma attack. Young children and those with compromised lung capacity may also have an adverse reaction after breathing in the first fumes of a hot bag of microwave popcorn.
http://www.wisegeek.com/is-microwave-popcorn-bad-for-you.htm