Sure, here's a CDC overview: http://www.cdc.gov/handwashing/show-me-the-science-hand-sanitizer.html They seem to be imperfect but better than nothing, and since people are surely not going to be washing their hands every time they cough, sneeze, or touch communal surfaces, supplementing normal handwashing practices with hand sanitizer seems like a probably-helpful precaution.

But note that this has turned out to be an accidental tangent since the "overhygienic" criticism was actually meant to refer to epistemic hygiene! (I am potentially also indignant about the newly clarified criticism, but would need more detail from Sam to find out what, exactly, about our epistemic hygiene he objects to.)