I peripherally heard about another Tylenol recall and assumed the recall was prompted by tainted medicine or something.  Anne just sent me a link to the story and it is apparently usability related.  The syringe-based dosing system, called SimpleMeasure, seems to be difficult to use.  Here is what NPR says:

the “SimpleMeasure” dosing system that’s supposed to make it easier to fill a syringe with the right amount of the grapey painkiller and fever-reducer is too complicated for some parents.