http://www.wxii12.com/news/22837954/detail.html this is a good article if you are worried about the safety in baby slings going on in the news. I believe the warnings being issued are more for the bag type slings sold commercially and the non adjustable wrap type slings.
No matter what kind of sling or baby carrier used the wearer needs to follow precautions to ensure the baby can breathe. Just like in a carseat or while holding the baby be careful not to let their chin smoosh against their chest. If they can not control their head it can close off the airway. Also like in a crib or anywhere don't cover up their face with anything. Make sure you can see the cute little face. :)