With a child in primary school, this is a subject that is never far away... I have taught critical appraisal classes using a study which compared "bug busting" (wet combing) and insecticides as treatments for headlice. This study concluded that insecticides were more effective.
The December Archives of Dermatology includes a "research commentary" on a paper in the BMJ from 2005, which also compares the two treatments and concludes the opposite, that is, that bug busting is best. But the commentary goes on to talk about the study design, and points out a number of places where the study design may have influenced the results.
Makes me think that headlice is indeed a good subject for critical appraisal classes.
The Archives of Dermatology commentary is Archives of Dermatology, 2006, 142, 1635-7, available to University of Leicester members from http://archderm.ama-assn.org/, with password available from me. There is a reply from the authors of the BMJ study, also, on p. 1651.