I just finished reading a lengthy expose on Pro-Publica, China Plays Tug-of-War With U.S. Inspectors Over Drywall, about Chinese and American drywall, tainted with sulfer, that causes extensive corrosion of metal components in walls, such as wiring; and also makes the occupants sick.
As a longtime sufferer of sulfer sensitivity, all I can say is this:
It looks like it is advisable to have the drywall that is delivered to your job site tested before it is installed in your home. At the very least somebody needs to give it a "smell test" to see if there is the tell-tale scent of rotten eggs.
There is no other way to protect yourselves from the fate of those people who tell their stories about contaminated drywall in their homes in the Comments below the article.
There are a lot more stories on ProPublica about the tainted drywall. Go to http://www.propublica.org/topic/tainted-drywall to read about the Lowe's settlement, now worth up to $100K to homeowners, and much more.
Here is an update from ProPublica on this problem: