Darshak Sanghavi doesn't think hand sanitizers work very well:
[W]e need to be realistic about what Purell can do to fight flu in the home and in public. To begin, the influenza virus mostly spreads via tiny droplets in the air (for example, from sneezes)not by dirty hands or surfaceswhich limits the role of Purell. It probably wouldn't matter even if flu transferred though hand contact, which is how most cold viruses spread. Though Purell kills them in the lab, hand sanitizers don't stop their spread in the real world. The average child touches his or her mouth and nose every three minutes, and both adults and children come in contact with as many as 30 different objects every minute. Even hospitals can't get staff to use Purell before seeing patients; it's impossible for day care staff, parents, or teachers to wash a child's hands 20 times each hour.
(Image: Creepy hand sanitizer ad from CopyRanter)