In the Gale Virtual Reference Library, I chose a volume on World War II.  Most of these volumes are above the level of my elementary patrons, but I could see their usefulness for older students.  I think that    
my older more advanced students could use it for research.  It is easy to get to the sections of the volume that I chose.
I went ahead and searched the question "What foods have zinc?".  Impressed with the number of volumes that it brought up.  The Listen feature is a great tool for those who either have a lower reading level or for those who learn better through audio.
Some of the other bloggers mentioned the use of these references as a tool for smaller libraries.  That is a great observation.  Being able to have the references as a tool without having them take up shelf space or come out of tight budgets.